Abstract: Terrain return decorrelation is generated by the changes of non-rigid objects themselves or the distances and viewing angles between rigid objects and radar. In this paper, the geometric and amplitude fluctuation model of terrain surface is built, andthen the characteristics of radar altimeter terrain return are simulated by the model. On this basis, an experimental program tomeasure the terrain return is carried out to verify the correctness of simulation results by using coherent pulsed S-band scatterometer. And the return data is processed cohenrently. The simulation and experimental results show that the terrain return incoherentloses depend on both the surface roughness and the distance that the aerialcarrier moved in a PRI.