The Mengentaolegai pluton of Horqin Right Wing Middle Banner in eastern Inner Mongolia consists of monzonitic granite, granodiorite and tonalite, belonging to high-K calc-alkaline shoshonite series. It has higher SiO<sub>2</sub>(72.03% in average), alkali-rich and relatively rich in K<sub>2</sub>O(K<sub>2</sub>O/Na<sub>2</sub>O=1.08 in average), lower Mg<sup>#</sup>(0.30 in average), and higher aluminum saturation index(A/CNK=1.08 in average). In ACF diagram, the rock is projected in S-type granite, with standard mineral of corundite, as well as muscovite and garnet in the rock, belonging to S-type granite category. It has lower amount of rare earth elements(ΣREE=120.76×10<sup>-6</sup> in average), stronger enrichment in LILE and depletion in HFSE((La/Yb)<sub>N</sub>=3.2～32.5), and negative Eu anomaly of variety(0.2～0.8). The trace elements in spiders web diagram and(La/Yb)<sub>N</sub>-<em>δ</em>Eu diagram show the enrichment of large ion lithophile elements(Rb, Ba), strongly depletion of high field strength elements(Ti), indicating the provenance of shell source. The pluton(Sr content in an average of 176.57×10<sup>-6</sup>, less than 300×10<sup>-6</sup>; Yb content in an average of 1.3×10<sup>-6</sup>, less than 2×10<sup>-6</sup>)belongs to the Himalayan-type granite, the source rocks may contain garnet and plagioclase granulite facies of the high pressure, which formed in the result of partial melting of thickened crust, the pressure of its formation may be between 0.8～1.5 GPa. In R<sub>1</sub>-R<sub>2</sub> and Yb-Ta diagrams, the rock belongs to syncollisional granite. The comprehensive analysis indicates that the Mengentaolegai pluton is a syncollisional shell source S-type granite, to provide the new evidence for the collisional time of the Siberian plate and North China plate.