The isothermal precision forging of a screw propeller was studied by means of numerical simulation and experimental forming. The deforming processes of the billet under two different forging patterns were discussed. The distributions of the flow line, the effective strain within the billet and the variation of the forging load during the forming process were analyzed. Results showed that there was a great difference of the effective strain existing between the blades and the wheel hub. The material flow and the distribution of deformation can be improved obviously by adding a core punch on the die. The distribution of deformation and forming load can be changed and controlled by adjusting the process parameters. The forging die was designed and manufactured according to the simulation results and perfect precision forgings have been acquired. Both of the simulation and the forming test showed that the precision forging of screw propellers could be formed with the isothermal precision forging satisfactorily.