Abstract: Inertia is the main factor which a ects the dynamic performance of a robot, due to the multi-close-loop structure of parallel robots, and the inertia of each driving shaft in joint space exists coupling property which will result in negative phenomena such as control overshoot and vibration especially when parallel robots work with high velocity and high acceleration. Thus, it is significant to study and evaluate the inertia coupling property of parallel robots. In this paper, based on the 3-PRS parallel robot, the inertia matrix is obtained through the principle of virtual work and an inertia coupling index is proposed, the coupling index represents the size of coupling inertia of each driving shaft when the robot works at different poses in the workspace. Then the distribution law of the index in workspace is analysed. Finally, a validation experiment is carried out on a typical 3-PRS parallel robot, the experimental results show that the load of each driving shaft will be changed by the coupling inertia, then the dynamic performance of the robot will be a ected by the variation of load. Meanwhile, the variation of load increases when the inertia coupling index becomes larger. The experimental results agree well with the theoretical analysis. This research result can be used to evaluate the dynamic coupling property of parallel robots, and it can also be used to optimize the structural parameters and design control parameters to further improve the dynamic performance of parallel robots.