In order to study the dynamics characteristics of the helicopter transmission shaft under real installation boundaries, a dynamic model of the helicopter transmission shaft, coupling and support with spring constraints was established based on the finite element software ABAQUS. Adjust the stiffness of the system boundary by modifying connection properties, and analyze the variation laws of the system's dynamic characteristics and steady—state dynamic responses across different boundary stiffness ranges. The research findings indicate that when the boundary stiffness is less than 1 × 107 N/m, the system exhibits two modes with the first—order vertical shaft—bending vibration pattern. As the boundary stiffness increases, the peak frequency of the system's first—order response rises. However, its response amplitude first increases significantly and then decrease slightly. When the boundary stiffness exceeds a certain threshold, only the first—order vertical shaft—bending mode remains in the system, and both the frequency and response amplitude of this mode barely change as the boundary stiffness increases.