Objective To solve the paper clamping difficulty caused by the low spring torque. Methods In the premise of meeting the using requirements, the parameters of spring in the paper-clamping system of the towel packaging machine, including spring wire diameter, middle diameter and the number of spring effective coils, were optimized by gradient optimal algorithm. Through stress analysis of the paper-clamping system, the gravitational torque of the portable plate and the spring torque before and after optimization were obtained. Results After optimization, the spring wire diameter, the middle diameter and the number of spring effective coils were increased by 13.78%, 23.37% and 25.28%, respectively. The optimized spring torque increased significantly. When the portable plate rotated 10 degrees upwards, the optimized spring torque was higher than the gravitational torque of the portable plate. Conclusion The optimized helical spring met the requirements of paper clamping and could ensure the accurate completion of paper clamping.