Abstract: Abstract: As one of the key components of the beet harvester, the beet top cutting mechanism plays a role in the first step of the harvest. The cutting quality has an important impact on the economic benefits of the sugar industries and farmers. In order to solve the problem that the existing beet top cutting mechanism can't adjust the cutting thickness while the mechanism runs, a new profiling top cutting mechanism was proposed, which consists of a parallel four-bar linkage, chain transmission, gear-rack mechanism, and profiling wheel. When the profiling wheel runs over the big beet top, the cutter attached on the rack will move down by the gear because the profiling wheel is elevated by the beet top. Therefore, the cutting thickness on the big beet top will be large. On the contrary, when the wheel runs over the small beet top, the cutter will move up because the profiling wheel is delegated. Then the cutting thickness will be small. Its working mechanism was analyzed. The kinematic model of this mechanism was established, and the equations of (angular) displacement, (angular) velocity, (angular) acceleration at the key points of this mechanism were derived. Then its kinematic simulation and optimization software was compiled based on Visual Basic 6.0, with which the effects of main parameters such as the sprocket transmission ratio, the gear pitch circle radius, the swing arm length, the profiling wheel radius, etc. on the cutting curve of the cutter and the cutting thickness were analyzed, Under the constraint that the cutting curve and cutting thickness should meet the agronomic requirements, a set of optimal parameters was obtained by the method of human-computer interaction, which was H=570 mm, k=2.4, Rf=180 mm, Rc=100 mm, L1=520 mm. The relationship between the linear velocity of the profiling wheel and the traction speed was analyzed and optimized by the genetic algorithm based on Matlab, and the optimization results were better than the experience values. These optimized parameters of the mechanism were used to build the three-dimensional solid models by the software UG. Then its virtual prototype model was constructed to simulate the kinematics by the software ADAMS. The results were that the cutting curves from the simulation and theoretical analysis were about the same verify that the theoretical analysis of the beet top cutting mechanism is reliable.