An analysis of petrography, major elements, trace elements and isotopic elements of Late Triassic-Early Jurassic syenogranites-alkali feldspar granites in Yichun area of Heilongjiang Province shows that most of these rocks have high temperature idiomorphic or conical quartz, accessory mineral fluorite, graphic texture and drusitic structure. Lithochemically, they are characterized by high silicon, enrichment of alkali, low calcium and magnesium and meta-aluminous to peraluminous nature. The REE distribution patterns show slight LREE enrichment with gentle right-oblique deviation and relative flat HREE pattern, sea-gull model of europium depletion, concentration of HFS elements such as Zr, Ce, Y and Ga, and depletion of Ba, Sr and Eu. Homogenization temperatures of quartz inclusions in these rocks are 750~950℃, indicating characteristics of high temperature hypabyssal magmatic passive injection. Syenogranites-alkali feldspar granites are rich in SiO2, K2O and Al2O3, and the values of δ18O are 5.1‰~10.3‰, belonging to granitic rock of normal or somewhat lower δ18O values. The values of ISr are relatively high and the values of of εNd are comparatively low, suggesting that original source materials of the source area are related to the metamorphic basement of the primeval lower crust, and also to a definite extent of crust-mantle magmatic mixing. Based on an integrated analysis, the authors hold that the Late Triassic-Early Jurassic syenogranites-alkali feldspar granites in Yichun area of Heilongjiang Province should belong to aluminous A2-type granites, and the tectonic background might be continental postcollisional collapse and extensional dynamic regime after the ultimate closure of the paleo-Asian ocean.