The flood current is one of the main sources of hydrodynamic conditions of debris flow. The formation mechanism of the hydraulics-erosion debris flow caused by the flood current is more complicated. To study the influence of different types of rainfall on the erosion and destruction process of debris flow in a flood process, flume experiments were conducted in Nanjiao gully. The big-scale flume was made, and the artificial rainfall device as well as the rear flow device was needed. The changes of precipitation as well as flood discharge were recorded in the process of surface erosion, slope erosion and trench erosion through the observation and description of the experimental phenomena. The erosion-destruction characteristics and mechanism of debris flow were studied based on the test results by moisture content and pore water pressure at different locations of the soils. The results indicate that in a flood process the gully erosion damage occurs before the arrival of the flood peak under the three types of rainfall. The antecedent rainfall reduces the cumulative precipitation of the soil damage, and gully failure occurs before the soil is saturated with "direct rainstorm type". The experimental results provide references for judging the rainfall and flood volume of debris flow occurrence, which has great significance for the study of rainfall pattern in the process of debris flow initiation.