Using metallographic examination， cold heading， and other experimental methods， this study investigates the optimization of the pinch roll groove system and clamping pressure in high-speed wire rod rolling processes to address the issue of coarse surface microstructure in piston rod steel S45C，which affects material fatigue strength and wear resistance. Analysis indicates that improper design of the pinch roll groove and inappropriate light/heavy pressure parameter settings lead to localized stress concentration on the steel surface， inducing coarse microstructure. Reducing the light and heavy pressure of the laying head pinch roll by 0.2 MPa significantly decreases surface stress and mitigates the degree of coarse surface structure. Optimizing the pinch roll groove by changing the contact between the laying head pinch roll and the red steel from point contact to surface contact alleviates clamping stress. Combined with reduced pinch roll pressure， this approach effectively resolves the coarse surface microstructure issue in piston rod steel S45C. In summary， the optimal production process involves using groove B with a heavy pressure of 0.35 MPa and a light pressure of 0.15 MPa. The resulting microstructure is uniform ferrite and pearlite， with no coarse structure at the edges. Customer validation confirms that the optimized S45C piston rod steel exhibits significantly improved surface microstructure uniformity， meeting high-precision application requirements and providing a reliable pathway for process improvements in similar products.