Abstract: The Laochang Pb-Zn deposit in Lancang, Yunnan Province is an important polymetallic ore deposit in the Sanjiang area in Southwest China. Based on a comprehensive analysis on the geological characteristics of the deposit, its origin is considered to be closely related with volcano-eruption sedimentation metallogenesis and post-volcanic exhalative hydrothermal reformation metallogenesis. The metallogenic fluid is the mixture of magmatic water and meteoric or sea water. The source of ore materials is crust-mantle mixture.