The Reshui granite is located at south to the Guidong composite granite. Zircon SHRIMP U-Pb dating, yields age of 162.8±5.8Ma (MSWD = 4.2) , suggesting its formation in the Early Yanshanian period. This granite is characterized by high silicon (average SiO2=76.32%), aluminum (average A/CNK>1.14) and phosphorus (average P2O5=0.41%), and potassium higher than sodium (average K2O/Na2O=1.32). It is also enriched in Rb, Th, Ce, Sm and Y, but depleted in Ba, Sr, Ti, Nb and Ta, with high Rb/Sr values (average of 28.5) and high Rb/Nb values (average of 19.8). Its light and heavy rare earth elements are not well fractionated, having flat chondrite-normalized REE patterns with clear Eu depletion (average δEu=0.14). The initial εNd(t) values of the rocks are generally low (averaging at -10.2) and the Nd isotope model ages are of Mesoproterozoic (averaging at 1777Ma). Source rock discriminating suggests pelite for the origin of the granite. All these above point to S-type granite affinity for the Reshui granite. Under the tectonic environment of subduction of the paleo-Pacific Plate in the Early Yanshanian period, which revivified the pre-existed Dadongshan-Guidong Fault, the Reshui granite was formed from a granitic magma probably generated by low extent partial melting of the Early Mesoproterozoic meta-pelite in the source.