In order to find out the problem of soil and water loss on the slope side of oil and gas pipeline operation in fully weathered granite area, this paper adopted the methods of measuring the boundary conditions of typical slopes in the field, collecting the data of gully depth and gully sectional area of slope erosion characteristics, sampling and testing rock and soil mass, and the indoor model rainfall test. The results showed that rainfall, slope length, slope, catchment area and geotechnical characteristics all affected the slope erosion of backfill soil in fully weathered granite pipe trench. Sediment yield and flow yield increased with the increase of rainfall intensity. The slope length, slope and catchment area were positively correlated with gully depth and gully cross-sectional area, and the gully depth and gully cross-sectional area increased with the increase of slope length, slope and catchment area. Through sampling, it was found that the relative content of particle composition of undisturbed soil was different from that of backfill soil, and the particle size distribution of the initial backfill soil was good. At the initial stage of rainfall scouring, the runoff of backfill slope mainly carried away silt and clay particles. Compared with the original soil, the porosity of the backfill soil in five years increased to 1.13 times, the soil permeability coefficient increased by one order of magnitude, and the cohesion in saturated state and internal friction angle decreased to 67.6% and 87.5% of that of the original soil, respectively. By finding out the influencing factors and their effects on slope erosion of backfill soil in fully weathered granite pipe trench, it could provide a basis for the subsequent slope treatment.