The low earth orbit satellite constellation is used for the discussed object in this paper. Regarding coverage performance as an important consideration, it states the general idea and method of the optimal design with the requirement of partial coverage for small satellite constellation in details. Based on the analysis of the key factors effect on the constellation performance, the optimal model is given by choosing the appropriate parameters with some constraints. For the design of different satellite planes, the potential and characteristic of constellation optimization are stated through the comparison between two orbit surface and three orbit surface constellation with some a specific task. Whereafter simulation and analysis is done. The result shows that the optimal model provided herein is of theoretical meaning and practical application.