This paper presents the kinetostatic analysis of pneumatic bending soft actuator coupling with revolute joint, aimed to discover the bending performance of soft actuator wearing on physical joint of human body as exoskeleton. First, a new pneumatic bidirectional bending soft actuator is designed and its mechanical characteristic is obtained by experimental tests. Then, the kinetostatic analysis based on the principle of virtual work is conducted on the proposed soft actuator in the cases of bending alone and coupling with revolute joint. Finally, the kinetostatic equations are solved, and thus the bending performance of the soft actuator bending alone or coupling with revolute joint is obtained. This research mainly reveals the influence of coupling constraint on bending motions of soft actuator and lays a theoretical foundation for the pneumatic bending soft actuator to be applied in assist exoskeletons.