The influence of process parameters on isothermal precision forging of a screw propeller is studied by means of FEM (Finite Element Method) simulation. The even degree of deformation, distributions of the flow line and effective strain within the billet and the forging load are analyzed. Notable difference of the effective strain is existed between the blades and the wheel hub of the screw propeller. Large deformation of the blade has been obtained, which is favorable for the blade strength. The material flow and the distribution of deformation can be adjusted by changing the process parameters and the forming quality can be improved. Both the forming temperature and punch speed have large influence on the forming load but less influence on the distribution of deformation. The result of simulation shows that the precision forging of screw propellers can be formed with the isothermal precision forging satisfactorily.