Effects of factors such as slope,surface soil texture,fertilization and crop cover with different rainfall intensities on phosphorus (P) losses in farmland runoff of the Dianchi Lake Watershed in Yunnan Province of China were studied through a rainfall simulation test using a red soil,one of the most widely distributed soils of the study area. Results showed that the runoff concentrations of total phosphorus (TP) and P losses differed with the slope,being highest when the slope was 18°. At two different rainfall intensities,the runoff TP and P losses had a similar decreasing trend as the surface soil texture became coarser,therefore applying the grit would decrease P in runoff from soils of farmland on slopes with heavier textures. With wheat as a crop cover the runoff TP concentrations and P losses were significantly lower than those of the bare soil. This showed that plant cover would greatly decrease P in runoff from the farmland of the study area. The TP concentration in runoff from the soil two days after fertilization doubled when compared with that from the non-fertilized soil,indicating that fertilization could mean a dramatic rise in P runoff if irrigation or heavy rainfall occurred immediately after application and that no fertilization before a rain and no irrigation immediately after fertilization would reduce runoff P loss from the farmland of the study area.