Zircon SHRIMP results indicate that the Caixi pluton in southwest Fujian was formed at 150±3 Ma. Caixi monzonitic granite is characterized by rich Si and alkali,weakly peraluminous nature, negative Eu (*Eu≈0.54～0.66) anomalies, enrichment of LREE, and depletion of Ba, Nb, Ta, Sr, P, Eu, Ti. They are characterized by Sr-Nd isotopic composition with (87Sr/86Sr)i being 0.710?462～0.712?265, εNd(t) -8.68～ -9.81 and t2DM1.51～1.61 Ga. The biotite of rocks is characterized by rich Al, Mg, and belongs to the type of crust-mantle mixed sources based on the triangle diagram of Fe2+ -Fe3+ -Mg2+.According to geochemical characteristics and petrological, mineralogical as well as geological data, it can be concluded that Caixi pluton be longs to the crust-source type granite formed by partial melting of the crust-derived rocks correlative to Proterozoic crust in the transformation from convergent to divergent tectonics. There were some materials mixed with the mantle materials in the process of rock formation.