Abstract: As an important source to obtain the information included in measured targets, the calculation accuracy in the Doppler phase became the key element to achieve real-time Synthetic Aperture Radar echo simulation technology based on FPGA. In the process of Doppler phase calculation, against the issues on the numerical root operation and the missing of specific prescribing devices in FPGA, to guarantee the simulation accuracy in the original data and meet the simulation need in bit-wide data, this paper considered Xilinx Virtex6 sx315t as the hardware platform, and adopted two common approximation method on Doppler phase calculation----- Taylor series expansion and CORDIC algorithm, then showed the corresponding program design and implementation for the Doppler phase fixed-point solving. In the meantime, this paper compared the simulation results from two method with MATLAB double-precision Theoretical data. Finally, the compared results proved the validity of accuracy in both Taylor series expansion and CORDIC algorithm.