The Jinchuan intrusion consists of pyroxene dunite, lherzolite, plagioclase lherzolite and olivine pyroxenite and hosts the third largest magmatic Ni-Cu-(PGE) sulfide deposit in the world. Petrography indicates that the crystallization sequence of the main rock-forming minerals of the Jinchuan intrusion was olivine → orthopyroxene → clinopyroxene → plagioclase. On the basis of rock textures and compositions of the dominant rock-forming minerals, the more precise composition of the parental magma of the Jinchuan intrusion have been obtained by using the thermodynamic code “MELTS”: 48.2% SiO2, 1.00% TiO2, 11.3% Al2O3, 12.9% FeO, 1.30% Fe2O3, 12.6% MgO, 10.1% CaO, 1.51% Na2O, 0.72% K2O, 0.04% NiO. The thermodynamic simulations also indicated the parental magma experienced two stages of fractional crystallization. In the first stage, crystallization of about 5% olivine and 4% orthopyroxene as well as sulfide liquid immiscibility occurred in a magma chamber at a depth of 10.9~12.5km (pressure is 3.3~3.8kbar). Stratigraphic zones from the base to the top of the deep staging magma chamber were formed due to gravity segregation, including olivine – orthopyroxene – sulfide – silicate liquid mush, olivine – orthopyroxene – silicate liquid mush, silicate magma. The silicate magma was squeezed out firstly to form some sulfide poor mafic intrusions or erupted to the surface elsewhere. The olivine – orthopyroxene – silicate liquid mush was squeezed to the shallower magma chamber at a depth of about 7.6~9.2km and formed the upper sequences of the Segment I and the upper pyroxene dunite in the Segment II of the Jinchuan intrusion. The olivine – orthopyroxene – sulfide – silicate liquid mush lastly intruded into the shallow magma chamber, where further crystallization of olivine, clinopyroxene, and plagioclase occurred and formed the main rocks and sulfide ore bodies of the Jinchuan intrusion. These results are consistent with the petrology and petrography of the Jinchuan intrusion, and also are consistent with the results of recent studies on the formation of the Ni-Cu sulfides.