The 2019 Shuicheng landslide was a typical landslide in that failure occurred in the slope deposits and there was a close correlation with the antecedent rainfall. The initiation mechanism was analysed using field investigations, laboratory tests and numerical simulations and the characteristics of mass movement were quantitatively assessed. The numerical results indicated that the infiltration of rainfall decreased the shear resistance of the slope and increased the pore water pressure and soil weight, resulting in a large deformation of the slope and a gradual deterioration in its stability. After saturation, as the pore water pressure coefficient (ru) approached 0.3, the overall safety factor decreased to 1 and failure eventually occurred. Quantitative mass assessment showed that the unique terrain aggravated the erosion and entrainment effects and that the inclusion of loose material and water promoted the movement of the debris avalanche by changing it into a fluidized state, resulting in a much larger landslide volume with a long runout distance. As a result, the volume of the failed mass, which was calculated by an unmanned aerial vehicle and terrestrial laser scanning modelling techniques to be c. 4.7 × 105 m3 in the source area, almost quadrupled to >2.0 × 106 m3.