Overgrazing interferes the grassland soil process of phosphorus (P) availability which is dominated by microorganisms, and topography also drives the P transformation and accumulation in soil. Soil microbial biomass phosphorus (SMBP) and enzymes involved phosphorus mineralization played important roles in soil P transformation. However, the effect of the interaction between topography and grazing rate on the participation of soil microorganisms in phosphorus activation process is not clear. In this study, the effects of grazing on the activities of soil alkaline phosphatase (ALP), acid phosphatase (ACP), phosphodiesterase (PD), and SMBP were investigated based on a ten-year grazing experiment (0, 1.5, 3.0, 4.5, 6.0, 7.5 and 9.0 sheep/hm²) on two topography treatments (slope and flat). This study hypothesized that 1) due to the soil water content (WC) of slope treatment is lower than the flat treatment, and so do soil nutrient properties, so the effect of slope treatment on SMBP is stronger than flat soil; 2) due to the slope soil lack of phosphorus than flat soil, so the activities of ALP, ACP, PD are higher than flat soil; 3) slope soil is facing higher nutrient limit caused by the difference of parent material, and water limit caused by topography, so, there may be different environmental factor driving the change of SMBP and enzymes. The results showed that topography, not grazing, significantly affected soil TP, P_O and Olsen-P. SMBP in slope treatment was significantly lower than that in flat treatment. SMBP was significantly increased by heavy grazing on flat treatment, but not on slope treatment. ALP and PD activities were only affected by grazing, while the activities of ACP were driven by topography. There was a complex relationship between the activities of PD, ALP and soil physical and chemical properties in the flat group, and there was a negative correlation between the activities of PD, ALP and grazing rate, while only the relationship between PD activities, phosphorus and TN was maintained in the slope group. The ACP activity of flat group and slope group was not related to soil chemical properties. Soil water content drives the difference between flat land and sloping land. Considering topographic factors, soil water content, P_O, TP and TN drive the change of flat soil, while slope soil is affected by soil water content, P_O and TOC. In conclusion, topography drives the response of SMBP phosphorus and phosphatase activity to grazing. This article indicates that, under grazing, the process of soil microorganism activities phosphorus is affected by different factors on flat and slope grazing treatments, and soil water content plays an important role.