Aiming at the problem of rope-biting hook under heavier load and serious abrasion of its roller in ropebiting mechanism of knotter, a calculation model of curved surface of cylindrical cam was built up by analyzing the kinematics of ropebiting mechanism in order to make the roller and cylindrical cam keep linecontact as well as ropebiting hook open and close according to sin acceleration law. By carrying out dynamic analysis of ropebiting mechanism and combining with the test of compression amount of compressing spring and tensile test of the rope, the statics model of ropebiting hook on the position of holding on to the rope was solved analytically, and optimum range of holdingon force of ropebiting hook was obtained which value is between 300.64N and 329.89N. The dynamic model of ropebiting hook was also solved analytically, and the contact force of cylindrical cam was between 240N and 330N when holdingon force of ropebiting hook is within optimum range. The peak value of contact force of cylindrical cam may be used to check contact fatigue strength of the roller, and guide material choice of the ropebiting hook and its roller. The field tests showed the roller installed on the rear of ropebiting hook didn’t have obvious abrasion after the kontter prototype finished 5000 bundles of rice and wheat straws according to predetermined preload force of compressing spring and initial pulling force of the rope. The result showed that the holdingon force of ropebiting hook was controlled suitably and linecontact cam improved contact load of the roller, which met the design requirement of impact resistance and antifriction.