Based on regional geological investigation and detailed petrological, contact relationship, isotope age and geochemical studies, this paper has dealt with geochemical characteristics and tectonic environments of granites in such rock bodies as Late Caledonian Baihua intrusive, Xiongshangou intrusive, Early Variscan Dangchuan intrusive and Huoyanshan intrusive in southern Tianshui area. The Baihua intrusive has low potassium content (K2O/Na2O=0.13～0.91), low aluminum (A/CNK=0.74～0.78), low Nb, Zr and rare earth elements (∑REE=107.71×10-6～191.13×10-6) and rich trace elements Cr, Ni, Y , Rb, Sr; the early rock of the Xiongshangou intrusive has low K2O (K2O/Na2O=0.33～0.42), whereas the late rock has rich K2O (K2O/Na2O=1.01～1.43) and trace elements Th, Hf, Nb, Zr; the Late Caledonian intrusives have some common characteristics: their rocks belong to tholeiitic-calc-alkaline series with enriched rare earth elements; they have no or indistinctive Eu negative anomalies and lowδ18O (δ18O=＋3.32‰), showing characteristics of “I-type" granite. The Xiongshangou intrusive derived its materials from the lower crust; the Baihua intrusive was formed in an island-arc tectonic environment; the Dangchuan intrusive is enriched in SiO2(SiO2=72.29%～73.40%), K2O(K2O/Na2O=0.86～2.01), and Al2O3(A/CNK=1.05～1.20); the Huoyanshan intrusive contains low SiO2 (69.70% on average) and high K2O (K2O/Na2O=1.14～1.88), Fe2O3+FeO and MgO. The Early Variscan intrusives show the following common characteristics: their rocks belong to shoshonitic series, with high Al2O3 (A/CNK>1.0) and abundant such large ion lithophile elements as Ba, Zr, Rb, Sm, Ta, Rb, Ba, Th and Nb; with high race earth elements, they have distinct negative Eu anomalies and low δEu （δEu =0.36～0.61) ; (87Sr/86Sr)0＞0.7070, with high δ18O (δ18O =＋8.89‰～＋11.08‰); they thus belong to medium strontium granite, with source materials derived from the earth's crust, belonging to “S-type" granite; they were formed in a pos t-collision tectonic environment or a post-orogenic tectonic environment.