The Hulunbair sandy grassland was used as the research object, and studied the effects of different grazing systems on phosphorus characteristic and phosphorus loss in surface runoff in arid and semi-arid grassland. We simulated rainfall with different intensities to study phosphorus concentration changing of surface runoff under three types of grazing systems such as no grazing, rotation grazing and free grazing. The effective mixing depth model was used to simulate the process of phosphorus loss from soil. Conclusions were as follows: Under different rainfall intensities, phosphorus runoff loss of free grazing system was the highest; its phosphorus loss was 1.31 to 1.5 times for no grazing grassland and 1.59 to 1.74 times for rotation grazing grassland. Particulate phosphorus was the major form phosphorus in the runoff and its content was 2.2 to 3.7 times higher than dissolved phosphorus. According to the result of experimental data fitting, the incomplete mixing model was better than the complete mixing model, and the model could simulate accurately for the case of higher rainfall intensity. The different grazing systems had significant influences on phosphorus losses in runoff under the rainfall intensity less than 1.5 mm/min. The phosphorus losses in rotation grazing grassland were the lowest. So, if we gently changed the grazing systems from the free grazing to no grazing and rotation grazing, the phosphorus loss situation would be decreased, which also would be helped for ecologically sustainable development in grassland.