[Objective] The mechanism of soil phosphorus loss from engineered slopes in a southwest alpine-subalpine region was studied to provide a theoretical basis for the restoration of the ecological environment on the same type of slopes.[Methods] The characteristics of total phosphorus (TP), sediment total phosphorus (STP), dissolved phosphorus (DP) migration, and their relationships with soil erosion, were studied under two slope gradients (30°, 50°) and four rainfall intensities (25, 45, 65, and 85 mm/h) using indoor simulated rainfall experiments and undisturbed soil removal.[Results] ① The average DP concentration of runoff from the engineering slopes was generally low and was less affected by rainfall intensity. The STP concentration was higher at the beginning of the rainfall and then decreased, or tended to be stable. ② The curves of the DP loss rate and STP loss rate from the engineered slopes had obvious differences under different rain intensities. When the rain intensities were 25 and 45 mm/h, the STP loss rate and DP loss rate from the engineered slopes were lower and more stable. When the rainfall intensity was 65 and 85 mm/h, the loss rate of STP and DP of the engineering slopes increased rapidly in a parabolic trend and tended to be stable. When the rainfall intensity increased from 45 to 65 mm/h, the loss rate of STP and DP increased rapidly. ③ The soil erosion rate was positively correlated with the DP loss rate, mean DP concentration, STP loss rate and concentration, and TP loss rate. The runoff rate was positively correlated with the DP loss rate, STP loss rate, TP loss rate, and mean DP concentration, but not with the STP concentration. The rate of TP loss from the engineered slopes increased gradually with the runoff rate and soil erosion rate in the form of a power function.[Conclusion] Rainfall intensity and slope gradient have significant influence on change of the dynamics of phosphorus loss from engineered slopes, and the trend of phosphorus loss first increases, and then decreases.