Lake Hongfeng is a reservoir located in the center of Guizhou Province, which was built in 1960. A 35cm sediment core HF1-2 was sampled from the lake for analysis in 2004. Some mineral magnetism parameters such as SIRM, χ_lf, IRM_20mT, χ _ARM, Hard, χ_fd% are measured, furthermore HIRM, ARM/SIRM, IRM_20mT/SIRM, ARM/χ_lf, SIRM/χ_lf are calculated from them. Based on magnetic measurements of the core, we can find the changes of magnetic properties influenced by soil erosion in the catchments during the past 43 years from 1960 to 2003. Combination with the results of analyses of¹³⁷Cs, grain size, TOC(%)and C/N, we divide the changes of soil erosion in the drainage area into several periods during these 43 years, the most seriously soil-erosion periods are during 1977 to1980 and 1987 to 1997. Compared with the rainfall data, we find the precipitation, especially summer precipitation may be the major reason of soil-erosion during 1977-1980, and there are some other unknown complex factors to affect the serious soil-erosion during period of 1987 to 1997.