Aiming to resolve the problem the space structure of rope cutting and releasing mechanism of knotter was very complex and the structure parameter influencing the motion of rope cutting and releasing was unknown. Kinematics analysis of rope cutting and releasing mechanism and other mechanism were carried out. The parametric design theory about rope cutting and releasing mechanism was established. The relationship of parameter matching between rope cutting and releasing mechanism and other mechanism was described. The important structure parameters influencing the motion of rope cutting and releasing were analyzed. The design requirements of rope releasing platform and cutting knife were calculated. The results showed that the distance between center of gyration of rope cutting and releasing mechanism and the rope releasing platform were 27~35mm, the distance between centre of gyration of rope cutting and releasing mechanism and the platform of rope cutting knife were 47~53mm, the cutting edge size of rope cutting knife was decided by the position size of platform of rope cutting knife. In order to verify the accuracy of the model, a modular rope cutting and releasing mechanism was designed and manufactured based on the range of key size of rope cutting and releasing mechanism. The designed rope cutting and releasing mechanism can adjust the position size and structure size of rope releasing platform and cutting knife, it was very convenient for the validation of structural parameters of rope cutting and releasing mechanism. The wheat straw baling test on the designed mechanism was conducted in the interior, eleven experimental groups were designed. Results showed that if the design size met the design requirements, the effect of rope cutting and releasing was good, otherwise the effect of rope cutting and releasing was poor. Therefore, it can be found that the calculating structural size parameters of rope cutting and releasing mechanism were confirmed to the requirements of D-knotter, and the model was accurate and it could guide the optimal design of D-knotter.