Diorite dykes intrusive in the Late Paleozoic basin were discovered in the Namling area in the middle part of Gangdese belt. Petrology, zircon U-Pb geochronology, major and trace element geochemistry studies were carried out to explore their petrogenesis and tectonic setting. Field geological survey and petrological studies show that diorite dykes are dominated by diorite, quartz diorite and pyroxene diorite, occurring as apophyses or stock, intruded into the Late Paleozoic strata. LA-ICP-MS zircon U-Pb dating obtained five groups of ages, 58.31±0.39 Ma, 60.53±0.96 Ma, 61.75±0.44 Ma, 65.02±0.31 Ma and 68.71±0.92 Ma, indicating that they were the product of magmatic activity from the late Late Cretaceous to the Paleocene. These dykes have relatively low content of SiO2 (49.58%~55.61%), high content Al2O3 (16.56%~17.38%), MgO (3.09%~5.48%) and Mg# (45~55), which belong to the series of high-potassic calc-alkalic to shoshonite and metaluminous. All samples are enriched in LREEs and depleted in HREEs with distinct right-dipping distribution and weak Eu anomalies (δEu=0.85~0.95). Their trace elements are relatively enriched in LREEs and large-ion lithophile elements such as Rb, Ba and K, depleted in high field strength elements, such as Nb, Ta and Ti, similar to those igneous rocks that form in subduction zone. The average temperature of zircon crystallization is 728℃ indicating that the magma had experienced melting process under the condition of nearly complete water saturation. Considering the temporal and spatial distribution of the Late Cretaceous to Paleocene magmatic rocks along the middle Gangdese, it is proposed that the northward subduction of Neo-Tethys was responsible for the diorite dykes in the Namling area. The rock is interpreted as resulting from partial melting of subduction sediments metasomatized with the overlying mantle wedge.