Laochang large-scale Ag-Pb-Zn polymetallic deposit in western YunNan is located in the basin of the Changning-Menglian rift which lies in the southern part of the Three-River metallogenic belt. As one of the most important deposits, previous studies of the deposit have been done and made a lot of researches, but the research of mineralization chronology is extremely weak. From the previous work, it is easy to find out that reaserch on Ⅳ ore clusters is rare. But Ⅳ ore clusters is the ore body through the mining area deep to shallow. So Ⅳ ore clusters is a key to study on mineralization mechanism. This paper we choose Ⅳ ore body which newly discovered in NW of Laochang Mining area and summarize past data. It is suggested that Laochang deposits belong to multi-complex causes, and it is mainly related to magmatic hydrothermal in late Hercynian period and concealed granite porphyry from late Yanshanian period to early Hymalayan period.