Abstract: In Loess Hilly Region, as one of the most important engineering measures for controlling soil and water losses, silt dams play an important role for reducing sediments and recording the historical variation process and characteristics of sedimentation in a small watershed. Combined with the history rainfall events and 137Cs contents of the silt dam and the surface soil samples of the inter-gully area and the gully side, sediment deposition cycle changes during the period 1959~1987 were analyzed. The sedimentation variation process and the sediment sources were studied in Guandigou watershed in Loess Hilly Region. The results show that in the initial stage of the silt dam construction, the sedimentation is very strong and then reduces greatly. The inter-gully area is the main sediment source area, which accounts for 70% of the total deposited sediment. There is great difference in sediment source between large watersheds and small watersheds.