To evaluate the reliability of space reusable locking device performing locking separation actions on orbit, aiming at the combined effect of spacecraft rendezvous and docking shock and performance degradation in the space environment, a reliability evaluation model considering interdependent competitive failure was established. Firstly, based on the function, structure and working principle of the device, the reliability characteristics were determined by the main fault modes on orbit. Secondly, considering both extreme and cumulative shock, a performance degradation model under shock was constructed. In view of the characteristics of small sample, high reliability and long life, accelerated degradation test and Bayesian method were implemented to estimate model parameters. Then, a reliability evaluation model was attempted based on the interdependent competitive failure theory of shock and degradation processes. Finally, taking a space reusable locking device as an example, the on-orbit shock simulation test and acceleration performance degradation test of the device were carried out. The model parameters were estimated by integrating the historical test data of similar products according to Bayesian formula, and the reliability function curve of the device was obtained. The result shows that in line with engineering practice, the device can still operate with a high reliability of 0.973 after 25 years on orbit. The proposed method and model proves to be capable of following closely the working conditions, and conducting a comprehensive reliability evaluation on the basis of the test and data available, providing an effective technical approach for mission reliability analysis and a theoretical basis for the design improvement and formulation of use strategy.