The deformation of a large crankshaft was simulated by the finite element with Forge software. The results show that the simulation deformation force and shape are not agreed with the practical results.Through analyzing the practical product and production situations, the practical crank web thickness is 1 mm thicker than nominal dimension, the diference between simulation force and practical deformation force is only 6.3% after the calculation of the deformation force. The crank web difference is due to uneven temperature distribution on the billet in the practical production situation .When using simulation technology , forging technician should concern about the changing of the various production conditions , and analyze the simulation result based on practical situation.