Sanjiang is  situated in the north area of the Guangxi Zhuang Automomous Region; at the middle beaches of the Xunjiang River; in the joint area of the three provinces: Hunan, Guizhou province and Guangxi Zhuang Autonomous Region. Sanjiang is surrounded by mountains with average elevation of 80-100m. Subtropical humid monsoon climate; with enough sunshine of more than 1600 hours annually; mild; with long frost-free period of more than 300 days.

Average annual temperature of 17-19C. Plenty of rain, concentrated in summers; annual precipitation of 1493 mm. Rivers of Sanjiang are Rongjiang River and Xunjiang River.