The soil and water loss caused by the construction service road in engineering construction is different from the traditional soil erosion. The construction service road changes the original natural slope morphology and hydrological process, resulting in vegetation destruction, surface exposure, and has formed road surface, excavating and filling slope and other erosion and sand production sites. The road cut and slope of side with loose structure have stronger and faster response to rainfall. Soil erosion caused by soil low grade roads accounts for a large proportion, so the study provides a basis for the prevention and control of soil erosion in the construction of roadways. Taking Bayi District, Nyingchi City, as the research object, using WEPP model to simulate and analyze the runoff and soil loss of under different precipitation conditions, different slope and slope length under engineering disturbance, so as to reveal the characteristics and key influencing factors of water and soil loss. The results showed that:(1) When the maximum rain intensity in 60 min (I₆₀) was 11.16 mm/h and the rainfall was 12.40 mm, runoff began to occur; When I₆₀ was in the range of 10 to 17 mm/h, the runoff was less than 0.50 mm, and the soil loss was less than 0.010 kg/m². When I₆₀ was more than 17 mm/h, I₆₀ had a linear relationship with the runoff and soil loss. (2) The runoff presented three stages of "rapid increase-slow down-gradual decrease" with the increase of slope. The lowest runoff was 56.98 to 58.00 mm when the slope was 5°, and the highest runoff was 76.19 to 77.01 mm when the slope was 30° to 35°. Soil loss presented two stages of "first rapid increase and then stable" with the increase of slope. When the slope was below 5°, the amount of soil and water loss was small, and the slope became stable after 50°. (3) With the increase of slope length, the runoff of backer slope decreases, while the runoff of non-backer slope remains stable. The runoff of backer slope was lower than that of non-backer slope after 50 m slope length, and the difference increases with the increase of slope length; With the increase of slope length, the soil loss of the backer slope showed a trend of "first rapid increase and then decrease", and the soil loss of the non-backer slope basically kept a uniform increase. The results can be used to analyze the driving mechanism of soil and water loss in slope after engineering disturbance in high and cold region.