The SHRIMP U—Pb ages for zircons from Caiyuanzi granites of number Ⅰand Ⅲ granites located in central Kangdian area, Huidong county, Sichuan province, southwest China are reported in this paper, and their respective ages are 1040.4±6.1 Ma(MSWD=0.53，n=18) and 1063.2±6.9 Ma(MSWD=1.15, n=11), highly in according with the time of the global Grenvillian orogenic movement.The major elements of Caiyuanzi granite have the characteristics of high SiO2 contents(mean value of 74.96%), peraluminous(A/CNK values of most samples higher than 1.1) , moderated alkali contents(mean content of Na2O+K2O is 6.5%), and low MgO(mean content of 0.17%), low TiO2(mean content of 0.28%), low CaO(average is 0.09%).Caiyuanzi granite with mean δEu value of 0.41 have low ∑REE(average value of 14 samples is 36.99×10—6), and the mean LREE/HREE and (La/Yb)N are respectively 3.34 and 8.57, implying slightly differentiation of LREE with HREE, and the chondrite normalized REE pattern display mew type of gentle curves skewed to the right. The large ion lithophile elements, such as Rb, Th, U, and La are relatively enriched, but Ba, Eu and high HFSE, such as Nb, Zr and Ti, are relatively depleted. These characteristics show that Caiyuanzi is typical S type of remelted granite.The geochemical characteristics of Caiyuanzi granite imply that the compositional material is made up of paragneiss which source rocks consist of pelite(main) and sandstone(secondary) in the source area. Calculating shows that the melt of Caiyuanzi granite which experienced strongly differentiation of biotite and plagioclase form from uppermiddle crust about 25km and 850°C under the spreading environment after the collision of blocks.The Dongchuan and Tangdan groups subducted and collide northward to Huili group during late Proterozoic along with Caiziyuan—Caimashui—Matang fault belt, resulting in the intrusion of Caiziyuan ophiolite and Caiyuanzi granite, and the eruption of intermediate—acidic volcanic rocks bedded in Tianbaoshan formation. The same collision and collage process maybe take place contemporaneously between Dongchuan and Kunyang group in central Yunan province. The basement of southwest Yangtze craton is probably made up of different epochal small blocks that experienced multiple spreading and collision.