Abstract: Maojia gully is located in the high mountain canyon area of the Western Sichuan and Eastern Tibet transportation corridor, with strong terrain cutting, steep mountains, large reserves and wide distribution of loose material sources in gully, and frequent short-term heavy rainfall, which has the possibility of large-scale debris flow disasters. The comparison scheme of the proposed Kangding to Xinduqiao expressway route selection needs to pass through Maojia gully, and the debris flow becomes an important factor controlling the geological route selection. In this paper, the morphological parameters of Maojia gully and its two large branches gullies were obtained by field investigation, remote sensing interpretation and GIS technology. By using the stormwater correction method, Matlab and Python were used to reveal the kinematic characteristic of debris flow, such as flow rate, velocity, depth of debris flow and overall impact force of debris flow in different parts of the channel and different rainfall frequencies, and systematically evaluated the level of threat of the two route selection schemes of Kangding-Xinduqiao Expressway by debris flow outbreak. The results show that when the rainfall frequency P=1%, Flow rate increases of 20.8 to 122.9% at the plugging and collapse points, the flow rate of N3 line 1# bridge (K line 1# bridge), N3 line 2# bridge and K line 2# bridge are 203.71 m³/s, 298.34 m³/s and 148.73 m³/s, and the affected height is 12.06 m, 12.18m and 11.64 m, respectively. There is a risk that the piers of the four Bridges will be silted attacked by debris flow impact, and debris flow early warning and management and protection measures will be vital.