Abstract: A weighted statistical evaluation model and corresponding simulation flow for evaluating the figure of merit of constellation service availability were suggested by dividing the satellite constellation into two groups according to whether the satellites in the orbital planes having fault satellite and by using probability and combination method.Using this model and simulation flow,an univariate study on the effects of variation of constellation configuration and orbital parameters on its service availabilities(SA) was performed.The results indicated that the number of orbit plane,relative phase factor and orbital height of the constellation have effect on its service availabilities.The proposed model has explicit physical meaning and can greatly reduces the evaluation time of SA merits.And the conclusions can help to select the optimal constellation configuration and orbital parameters in conceptual design phase.