Abstract: Based on optimizing the die exit structure by setting a damping block in the flow channel to balance the flow velocity at the outlet of die, the extrusion swell in the extrusion process of the tread rubber was improved. The extrusion process of the rectangle tread rubber when the damping block was set at different positions was simulated and calculated by using the Polyflow software, and the corresponding extrusion expansion of rubber products were analyzed. Also, the influence of the damping block position on the profile of the extrusion swell was studied by simulating the pressure and velocity distribution of the rubber melt in the die. Then, the extrusion experience with home-made extrusion die was carried out, and the cross-section profile of the extrusion swell of experience was coincided with that of simulation. It demonstrated that the optimization design project and simulation were reasonable. The simulation and experience results indicated that the damping block could regulate and control flow velocity of rubber melt at the outlet of die and improve the extrusion swell.