The main mission of early warning system of LEO is to detect and track the midcourse missile, so the problem of the staring sensors coverage of LEO is researched in the article. Firstly, the models of staring sensors in different space altitudes are built based on their operating range and turning of lens. Secondly, according to the limitation of the grid analysis method, the rule of grid partition is improved and the function relation of the latitude and longitude alternation、the grid precision of grid partition in the different latitudes is set up, the computing process of coverage analysis is put forward based on the typical coverage performance index. Finally, some space coverage performance of a typical constellation is educed through simulation, and the result shows that the coverage models and the improved grid method are available and effective.