Compaction is considered to be a common mechanism for the expulsion of interstitial liquid from the crystal mush when the abundant crystallization of Fe-Ti oxides during the mid-late stage of the solidification of layered intrusions. However, the efficiency of compaction is often different from layer to layer, and the main factors controlling the efficiency of compaction is not clear yet. The Neoproterozoic Wangjiangshan intrusion is a large and well-differentiated layered intrusion in the northern margin of the Yangtze block, and is composed of dunite, pyroxenite and troctolite in the lower zone (LZ), gabbro and gabbronorite in the middle zone (MZ) and diorite in the upper zone (UZ). The ~2000-m-thick MZ is the main part of the Wangjiangshan intrusion, and can be further divided into MZa and MZb based on the occurrence of Fe-Ti-V mineralization. Mineral composition and texture of rocks are distinct from the MZa to MZb, indicating that the different rock units in the MZ may have different mechanisms and different degrees of expulsion of interstitial liquid from the crystal mush. Therefore, we collected samples from the MZ of the Wangjiangshan intrusion and analyzed the crystal size distributions (CSDs) and spatial distribution patterns (SDPs) for clinopyroxene and plagioclase, in order to study the expulsion mechanism of interstitial liquid from crystal mush and its efficiency. Methods: Three samples from the olivine gabbronorite unit, four samples from the gabbronorite unit of the MZb and five samples from the oxide gabbro unit of the MZb were selected for the CSD and SDP measurements for plagioclase and clinopyroxene. Results: Plagioclase and clinopyroxene of the olivine gabbronorite unit and the gabbronorite unit of the MZb, and the oxide gabbro unit of the MZb overall show parallel CSD curves and the negative correlation in the SDP plot, suggesting that the interstitial liquid was expelled by the mechanical compaction in these three units. On the other hand, the fraction of trapped liquid (FTL) of samples from the olivine gabbronorite unit, the gabbronorite unit and the oxide gabbro unit are from 28% to 33%, 14% to 23%, and 7% to 12%, respectively, calculated by the equilibrium distribution method using whole-rock composition, indicating that different degrees of mechanical compaction for these three units. Plagioclase less than 0. 1 mm of the olivine gabbronorite unit has a high aspect ratio from 5∶1 to 11∶1, and the CSD curves have intercept from 2. 23 to 3. 78 with the characteristic length from 0. 29 to 0. 45, suggesting a high rate of magma cooling. This results in a low compaction rate with a maximum of 0. 33 m/a and a high rate of crystal accumulation with a minimum of 0. 27 m/a of the crystal mush, leading to an inefficient mechanical compaction and a low degree of expulsion of interstitial liquid. Plagioclase less than 0. 1 mm of the gabbronorite unit has a low aspect ratio (< 5∶1), and the CSD curves have intercept from 1. 31 to 2. 60 with the characteristic length from 0. 43 to 0. 58, suggesting a low rate of magma cooling. This results in a high compaction rate with a maximum of 0. 54 m/a and a low rate of crystal accumulation with a minimum of 0. 18 m/a of the crystal mush, leading to an efficient mechanical compaction and a slightly higher degree of expulsion of interstitial liquid. Plagioclase less than 0. 1 mm of the oxide gabbro unit has a low aspect ratio (< 5∶1), and the CSD curves have intercept from 0. 49 to 1. 60 with the characteristic length from 0. 53 to 0. 69, suggesting the lowest rate of magma cooling. This results in a high compaction rate with a maximum of 0. 95 m/a and a low rate of crystal accumulation with a minimum of 0. 13 m/a of the crystal mush, leading to a more efficient mechanical compaction and a much higher degree of expulsion of interstitial liquid. Conclusions: The interstitial liquid of the three units in the MZ of the Wangjiangshan intrusion was expelled to varying degrees by the mechanical compaction. Mechanic compaction for samples from the olivine gabbronorite unit of MZa is inefficient, due to the fast magma cooling rate and the small density contrast between the cumulus and the interstitial melt. With the decrease of cooling rate, the compaction efficiency of the gabbronorite unit of MZa and oxide gabbro unit of MZb gradually increases. Simultaneously, abundant crystallization of Fe-Ti oxides may progressively increase the density contrast of the cumulus and the interstitial melt, resulting in a further increase of the compaction efficiency of the oxide gabbro unit. This study indicates that the efficiency of mechanic compaction of layered intrusions is mainly controlled by the cooling rate of magma and the density contrast of the cumulus and interstitial melt, with a distinct enhancement by the low cooling rate of magma and abundant crystallization of Fe-Ti oxides.