The under-filling defect of the I-beam, one of the typical defects on a heavy truck front axle in the precision roll forging process and die forging process was studied. Firstly, the design of the precision roll forging process for the I-beam of the front axle was described. Then, the finite element numerical simulation analysis model was established with Deform-3D, and the influence of the thickness on the I-beam in the third step and the friction factor in the third and fourth step on filling percent of the die cavity was analyzed. Lastly, optimization for the precision roll forging process of the heavy truck front axle was finished. The optimized simulation results show that the I-beam forms well and can be filled fully to meet the requirements of design drawings.