In the present paper, the precision forging of an impeller was studied by means of numerical simulation and test forming. Based on the structure and dimension of the impeller, the combination structure was used in the forging die to obtain the extrusion deformation. The forming processes were simulated with DEFORM-3D for different billet dimensions and processing parameters. The parameters, which could ensure the forming quality of the impeller, were determined by the calculations and analysis. The die structure and the billet dimensions were determined according to the simulation results, and the forging die was designed and manufactured. The billet with semi-solid microstructure was produced by means of the direct heating-isothermal treatment. The forming was conduced in an YX-315F hydraulic press, and the precision forgings of the impeller were produced successfully. Both of the simulation and the forming test show that the impeller forging can be formed with the combination structure die and the extruding forming stale satisfactorily. The ideal parameters to produce the precision forgings of the impeller are: billet temperature at 625°C, die temperature at 450°C and punch speed at 20mm/s. Under these conditions, forgings of the impeller can be produced with plump blades, smooth outer surface, and good flow line. This can match the requirements of the precision forging of impellers.