Abstract: The accumulation behind the debris flow gully dam is a good material for studying debris flow information. Based on the field investigation, 10 typical debris flow debris flow debris flow debris flow debris flow debris flow debris accumulation samples were collected in Wudu District of Longnan, Gansu Province, and the particle size and debris flow dynamics were analyzed. The results show that: 1) the particle size composition of each sample is quite different, and most of the dominant components are obvious; 2) The average particle size is between 8.42～40.35 mm, the sorting coefficient is between 10.21～35.27, the skewness is between −17.25～25.26, and the kurtosis is between 13.73～31.31; 3) The fractal dimension of particle size is between 2.40 and 2.72; 4) Particle size parameters, curvature coefficient, nonuniformity coefficient and fractal dimension have different degrees of correlation; 5) The gullies can be divided into two groups and three categories according to the Q-type clustering of grain size index; 6) The volume density of debris flow represented by the accumulation body is between 2.04～2.26 t/m³, and the average velocity is between 0.96～13.20 M/s, which can well correspond to the clustering results. Compared with loess sediment, paleoflood sediment and offshore surface sediment, the average particle size is three orders of magnitude larger, the sorting property is obviously poor, and the values of skewness coefficient and kurtosis coefficient are obviously larger; The fractal structure is good, and the fractal dimension value is relatively concentrated, which is obviously larger than that in Loess and marine sediments; The most powerful impact force on the dam body is huomiangou, the stronger are jiajiagou and Dachuang gully, and the rest are weak.