The experiment was conducted in the Stipa breviflora Griseb. desert steppe, Inner Mongolia (41°47′17″N， 111°53′46″E，1450m sea level) from 2002 to 2004.The objectives were to test the integrated influence of different stocking rates on species diversity and productivity with fenced sheep grazing. The results showed that the species diversity changed in the second year under different stocking rates, and the average species diversity decreased with the year, but there was no significance. The maximum species diversity occurred at a stocking rate of 1.027 sheep/(hm²•a). The aboveground net primary productivity of the plant species occurred with equal-compensatory growth when the stocking rate was below 1.027 sheep/(hm²•a), but it decreased rapidly when the stocking rate increased. Therefore, the optimum stocking rate is 1.027 sheep/(hm²•a) in this kind of steppe. The results in this study support the single-peak model with minus quadratic function in the relationship between species biodiversity and productivity of the plant community, that is, that maximum species diversity occurs at the moderate plant productivity.