Abstract: The interdependence and fusion of cyber system and physical system is the main characteristic of cyber-physical power system（CPPS）. This paper proposed function failure models for monitoring function and control function, and studied direct/indirect cyber-physical impact. Then, a method for calculating the availability of circuit breaker considering control function impact is presented. Based on analysis of power cascading failure caused by monitoring function failure, a reliability assessment method of Power CPS considering monitoring function and control function is given. Finally, the different impacts to Power CPS caused by different cyber failures are analyzed through case study, the result shows the feasibility, necessity and effectiveness of this research.