The dynamic performance and inertia coupling strength of a 3T1R decoupling parallel mechanism (PM) were analyzed. Firstly, the kinematics of the mechanism was established, and the forward kinematics and inverse kinematics were given to obtain the Jacobian matrix of the moving platform, where the velocity and acceleration of each link and the moving platform were derived. Based on the Newton-Euler method, the inverse dynamics model of the mechanism was established considering the gravity of the components and the external load. The driving forces of the PM were solved, which was then verified by ADAMS dynamics simulation. At the same time, the influences of acceleration and the attitude angle of the moving platform on the driving force of the branch chain were analyzed based on the established dynamics model and the analysis results can provide theoretical basis for trajectory planning of the mechanism. Finally, an inertia coupling evaluation index was proposed based on the inertia matrix in the joint space, which represented the coupling strength of the driving branches when the PM worked at different poses in the workspace. Then the distribution law of the index in workspace was studied and compared with that of the Quadrupteron mechanism before decoupling. The results showed that the decoupling of the PM not only reduced the coupling strength between the branches, but also made the distribution of the coupling strength in the workspace more consistent, which improved the isotropy of the dynamic performance of the mechanism.