Artificial rainfall experiments were carried out to investigate the distribution characteristics of nitrogen and phosphorus in runoff system of urban backfill soils of different slope gradients. The results showed that soil slope had a significant effect on hydraulic distribution. Specifically

when the slope was 4°

the proportion of surface runoff

side-percolation flow

and down-percolation flow was 72.5%

25.3%

and 2.3%

respectively. However

the surface runoff was prominent when the slope reaches 8°. Furthermore

for the slope of 4°

the percentage of total nitrogen in the surface runoff

side-percolation flow

and down-percolation flow was 69.7%

26.1%

and 4.2%

respectively. Meanwhile

the proportion of total phosphorus was 77.6%

22%

and 0.4%

respectively. The proportion of nutrients in surface runoff increased slightly with increasing slop gradient. Therefore

in the design of backfill soil

smoothing the surface would be beneficial to improve soil water infiltration

reduce surface runoff

and decrease nitrogen and phosphorus pollution of urban backfill soil.