In recent years, there has been few research on the genesis and evolution of Mesozoic granites in southern Zhangguangcailing, Heilongjiang Province. Therefore, the systematic study of isotope chronology and rock geochemistry will help to deepen the understanding of the evolution and geodynamics of Early- Middle Jurassic tectonic magma in southern Zhangguangcailing. The early Jurassic granites in the southern part of Zhangguangcailing are mainly composed of biotite quartz diorite, biotite granodiorite and biotite monzonite granite. The LA- ICP- MS zircon U- Pb dating for the three samples yields an age of 172. 7~182. 4 Ma, suggesting the Early Jurassic in age. The biotite quartz diorite and biotite granodiorite are characterized by a large number of mafic microgranular enclaves, calc- alkaline, A/CNK value less than 1. 1, weak negative Eu anomaly (δEu=0. 55~1. 03), indicating that they belong to I- type granite and are of genetic mechanics of mantle and crust mixing. The biotite monzonitic granite is peraluminous, high K and Ca and alkaline rock, and characteristic of S- type granite. Middle Jurassic biotite tonalite rock is characterized by rich mafic microgranular enclaves and A /CNK value less than 1. 1 (0. 88 to 0. 93), suggesting I- type calc- alkaline granite. The syenogranite and alkali feldspar granite are characterized by high silicon (SiO2=76. 89%~77. 82%), rich alkali (K2O+Na2O=6. 36%~8. 5%), and rich Fe and poor Mg (FeOT/MgO=6. 2~20. 6), high total REEs, Eu negative anomoly (δEu=0. 01~0. 74), with enrichment of LREE and depletion of HREE, suggesting A2- type granite. The study of the Early- Middle Jurassic granites in the southern part of Zhangguangcailing shows that in the early Early Jurassic (172. 7~182. 4 Ma), the subduction of the Paleo- Pacific plate and the subsequent detachment effect of the lithosphere resulted in uplift of the mantle and the bottom plate of mantle magma resulted in partial melting of the ancient crust and the new crust, thereby forming granite with the mixed feature of crust and mantle. In the late Early Jurassic (172. 7 Ma), the Jiamusi plate in the east collided with the Zhangguangcailing block, forming the biotite monzonitic granite. In the early Middle Jurassic (168. 1 Ma), the continous subduction of the oceanic plate in the east continued formed biotite tonalite with characteristic of the crust and mantle mixing. In the late Middle Jurassic (166 Ma), the tectonic setting changed gradually from extrusion orogeny to post- orogenic extension.