The Laochang polymetallic deposit is one of the most important deposits in the south of the Sanjiang metallogenic belt and belongs to the polygenetic mineral deposit with superimposed metallogenic systems between the SEDEX ore-forming system and the hydrothermal porphyry metallogenic system. Based on an analysis of the typical minerals and rocks in different mineralization systems in the aspects of S, Pb, H, O isotopes, the authors compared the differences and similarities of deposit's geochemical characteristics in the different metallogenic systems, and the result shows that mineral sources of the two metallogenic systems were characterized by inheritance, regeneration and multiple sources. In the SEDEX ore-forming system S was mainly derived from volcanic hydrothermal solution, Pb mainly came from ancient continental crust basement and volcanic rocks, and ore-forming fluids were mainly derived from mixed magmatic water and brine as shown by H-O characteristics. In the porphyry-hydrothermal mineralization system, S mainly came from the mantle or crust-mantle magma homogenization, Pb was mainly from the crust-mantle mixing, ore-forming fluids were mainly derived from magmatic water and meteoric water, and ore fluids of the late stage had more characteristics of meteoric water. ⁸⁷Sr/⁸⁶Sr ratios of granite porphyry are between the average of the crust and that of the mantle, whereas isotope data of Sm-Nd is close to the EMⅡ, suggesting that the magma source was in the crust-mantle transition zone.