The Gejiu in Yunnan Province, south China, is the largest felsic intrusion-related Sn-polymetallic ore field in the world. The Shenxianshui in western Gejiu district occurs as a stock, and consists of Si, alkali-rich, and Ca, Mg-poor alkali feldspar granite. Chondrite-normalized REE distribution pattern shows pronounced negative Eu anomaly and LREE enrichment. Bulk geochemistry characteristics indicate that the Shenxianshui is highly differentiated A-type granite. Zircon LA-ICP-MS Concordia age of (81.7 ±0.6) Ma indicates that the Shenxianshui granite occurred at Late Jurassic. Regional geology and bulk rock geochemistry indicate that the Shenxianshui alkali feldspar granite formed at an extensional tectonic setting during Late Yanshanian.