Considering the joint effects from wind and wave, a simple load model of offshore wind turbine system was built. According to the simulation method of nonlinear regular wave based on the stream function theory and Morison equation, the program used in the extreme wave loads simulation and calculation was coded using C++/Fortran mixed-program. A nonlinear wave simulation was obtained using this program and the simulation results are good in agreement with those obtained by the foreign program used in the calculation of the wave loads on the offshore wind turbine. This validates the simulation and calculation model of the extreme wave loads. At last, the extreme wave loads from the wave mentioned above on a tower were calculated using the developed program. An available method of calculating extreme wave loads on the offshore wind turbine was provided by this paper.