In this paper, the received signal of accelerated moving target on three directions is modeled as a cubic phase signal (CPS) for distributed space-borne SAR, and the cubic phase function (CPF) method is used to estimate the parameters of accelerated moving target. The simulation results show that the cubic signal model is reasonable, and CPF provide a better performance for the estimations of velocities and accelerations of moving target for SAR than the method of high order fuzzy function (HAF), especially in the conditions of low SNR.