Hutouya pluton is a middle-late Triassic (Late Indosinian) granitic body in Qimantage minerogenetic belts, which mainly composed by biotite-monzonitic granite, syenogranite and little granite with diorite inclusion. The rocks have high silicon (70.71%～77.67%), high potassium (4.7% in average) and are rich in alkali (Na2O K2O=7.86%～9.1%), and the average value of K2O/Na2O is1.36, the value of A/CNK spread within the limits of 0.91～1.05. The rocks belong to high-K,cala-alkaline series peraluminous granitoids. The rocks have middle ∑REE values with an average of 120.10 μg/g, values of δEu within the limits of 0.04～0.47, values of (La/Yb)N spread among1.52～8.06, the rare earth patterns of rocks/chondrite shows the right deviation of ‘V’ type with the character of negative Eu and flat HREE. The rocks are rich in LIL and HFS, and evident negative anomalies of Ba, Sr, Nb, Ti, P. According to the character of regional geology, the diagram of A/FM-C/FM and the spider pattern of trace elements, the author infers that the Hutouya granite is the production of partly fusion of original resource and participation of crust. Based on tectonic history and the diagram of structure environment, the Indosinian granitoids(including Hutouya pluton) formed in post-collisional tectonic setting of syn-orogenic stage. The formation mechanism of Indosinian granitoids is as follows: between later Permian and earlier Triassic, Animaqing ocean basin downthrust to the south margin of Kunlun micro block and form the tectonic setting of syn-collision or within plate, the original basic rock closed association with mantle-derived magmata also developed in this period; during the middle-late Triassic, the pressure stress become weaker after the main collision, and the depth pressure got lower, that made the crust thicker and hotter, and melting point of rocks lower, finally the basic magmatite house was partly melting, and the melt emplace into the upper crust in the open tectonic setting.