Abstract Dynamic coupling of active branches of parallel manipulator under joint space, which is caused by the structural characteristic of multiple kinematic chains, will affect the overall dynamic performance under high speed motion. To study and reflect the dynamic coupling of active branches of parallel manipulator, a dynamic coupling strength coefficient was defined firstly. The coefficient, which has unified scale, is suitable for describing the dynamic coupling characteristics of general parallel manipulators. Second, the dynamic coupling strength coefficient was applied to study the dynamic coupling characteristics of a 2(3HUS+S) type parallel manipulator, and the results, which were verified by experiments, were obtained under a constant trajectory. Finally, variation of the dynamic coupling strength coefficient along with the structural parameters was calculated, and strategies to reduce the coupling effect were also proposed.