The Precipitation Radar (PR) on board the Meteorology Satellite is an active remote sensing radar to measure precipitation from space. The PR, operating at dual frequency, still under study, is designed to be an active phased array that allows a fast and sophisticated cross-track scanning. In order to confirm that PR functions properly and meets the performance requirements to quantitatively measure three-dimensional precipitation distribution from space, especially the feasibility and applicability of our waveform, the simulation of PR's receiving echoes is strongly required. In this paper, a space-based meteorological particle distribution model, which can mostly reflect the truly distribution of the particle's size distribution, is built. Then we calculate the phase variance of PR echo caused by particle's movement. At the end of this paper, we estimate the surface clutter interference through antenna side lobes, assuming a surface scattering model and a realistic antenna pattern for a phased array antenna.