It is key issue to accurately simulate the radar echoes of offshore wind turbine and extract micro-Doppler features, and they can solve the reradiation interference of offshore wind farms to neighboring radar stations. Aiming at the problem that the existing algorithms treat directly the sea surface background of wind turbine as a planar good conductor and are too simple. In the meanwhile, the traditional equally spaced scattering point model cannot characterize the complex surface features of the wind turbine blade. Therefore, we introduce a multipath model with a forward complex reflecting coefficient model of rough sea surfaces in radar echoes simulation, also build 3-D scattering point equivalent model of wind turbines. So, a numerical simulation algorithm for radar echoes of offshore wind turbine based on time domain echo electric field is proposed. According to the though of discrete electric field equation of RWG function in the method of MOM, we establish a 3-D scattering point equivalent model of wind turbine. Considering the distortion effect when the electromagnetic wave acts on the sea surface, the time domain return electric field solution equation under a forward complex reflecting coefficient model of rough sea surfaces is derived. We perform vector superposition short-time Fourier variation about radar echoes, and obtain the simulation results of the radar echoes of the offshore wind turbine. By comparing simulation results and experimental results of the scaleddown model, it verifies the correctness of our algorithm. Finally, the micro-Doppler characteristics of the wind turbine echoes under the sea surface background are analyzed in comparison with those under free space,and it prove that the sea surface background cannot be neglected. The influence of sea state about micro-Doppler shift are further analyzed by controlling a single variable. It is，the root mean square of the wave height is negatively correlated with the Doppler shift. These results also provide theoretical reference for the subsequent identification and filtering of offshore wind turbine echoes.