The development and utilization of wave energy is inseparable from the wave energy converter, and its stability is an important condition for operation. Heave is the biggest factor affecting the stable power generation of wave energy converters. The key method to solve this problem is to install a suitable heave plate. Therefore, the design of the heave plate is particularly important. Based on a new type of horizontal rotor wave energy converter, this paper proposes three different shapes of heave plate design schemes and completes the calculation and modeling of the engineering prototype. First, the three types of heave plate devices were numerically simulated using hydrodynamic calculation software to compare their stable performances and verify the feasibility of the scheme. Subsequently, an experimental model was made according to the parameters of the engineering prototype, and a tank experiment was carried out under the same working conditions to further study the influence of the heave plate installation distance on the stability of the wave energy generator. The results showed that when the distance was between 10 mm and 20 mm, the average amplitude change was large, and when the distance was between 20 mm and 30 mm, the average amplitude change was small. Therefore, the installation distance should be between 20 mm and 30 mm. In the case of the same heave plate area and installation distance, the average amplitude of the chamfered heave plate device was smaller than the other two types, indicating that its stability was better. The optimization of the shape and installation distance of the heave plate proposed in this study has obvious effects on improving the stability of the device and provides a reference for the design of the wave energy converter device.