Phosphorus loss by runoff and its affect factors were studied in various upland fields form yellow soil of Guizhou province.The results showed that with a rainfall simulation experiment particulate P and ortho P losses with surface runoff in various upland fields were different, which the phosphorus losses in the upland field with high fertility were obvious. The important factors affecting particulate P loss were the contents of available P and <0.001mm clay of the soil. The other, the main factor affecting ortho P loss was the soil available P content. In addition, higher rainfall intensity increased particulate P loss so as seriously to enhance the soil P loss, while lower rainfall intensity increased ortho P loss.