Dating the sediments age with ¹³⁷Cs, using rainfall data since 1953, the grain size cycle characteristics of hydatogen sediments in natural check dam of loess depression are analyzed. Results showed that the 4 m depth of sediments was formed in the recently one hundred years, and its material was mainly coming from flood erosion. Rainfall was the main factor affecting the particle size of sediments. Flood sediments was mainly composed of coarse silt, while the ratio of medium sand was low and the coarse sand was not found. The section of sediments had distinct sedimentary layers, which have recorded at least 42 flood events. The grain sizes of flood sediment layer in different periods changed significantly, which showed the rules of watershed erosion and precipitation variation in the recently one hundred years.