In the Hainan Island, the Middle Triassic syenite—granite suite, with outcropped total area of 516 km2,was distributed along the Lingshui—Longgun deep fault and on the southeast side of the Baisha deep fault. It is composed of quartz monzonite, quartz syenite and syenogranite.The suite shows a large variation in their SiO2 contents (SiO2=58.40%~76.14%), and is riched in alkali and K2O, with Na2O+K2O=7.10%~11.49% and K2O=3.78%~7.91%, It belongs to shoshonitic alkaline series. Their A/CNK values range from 0.88 to 1.12, most rocks of the suite belong to subaluminous series(A/CNK mostly <1). Their FeO＊/MgO ratios are generally high (3.14~87.13). Their abundances of rare earth elements change greatly and most of them are relatively high, with REE=125.5×10-6~980×10-6. The REE patterns display rightinclined, with mediumdistinct differentiations between light and heavy rare earth elements. The δEu values are 1.80 ~0.06, with positive or insignificant Eu anomaly for the early units, such as the quartz monzonites and quartz syenites, but obvious negative Eu anomaly for the late syenogranites. Rocks of the suite have high Zr, Hf, Zn, F concentrations and (Ga×104)/Al ，Nb/Ta ratios(20.36 on average). The Ba contents of the early unit rocks are higher but which of the late rocks are lower. Normalized trace element spidergrams demonstrate that negative Sr, P and Ti anomalies are gradually enhanced from early units to late units. Their isotopic compositions of Pb, Sr and Nd are relatively homogenous and are consistent with which of the Middle—Late Triassic mafic intrusions, with n(206Pb)/n(204Pb)=18.487~18.586，n(207Pb)/n(204Pb) =15.606~15.655, n(208Pb)/n(204Pb)=38.503~38.635, mean \[n(87Sr)/n(86Sr)\]i,εNd（t）and T2DM is 0.71067, -6.88 and 1575Ma respectively. The suite is classified in Atype granitoids, In which the granites were probably generated from quartz syenitic melt through crystallization differentiations of minerals, such as feldspar, hornblende, apatite, ilmenite, sphene, etc. And the quartz syenitic melt may be derived in the deep crust mainly by differentiation of alkali basaltoid magma which was originated from the EM Ⅱtype enriched mantle. The suite is considered formed in a postorogenic extensional tectonic setting.