The invention provides an accurate hidden failure model-based cascading failure risk evaluation method for a power transmission system. The method comprises the following steps: firstly, building a hidden failure probability model according to the condition that different hidden failures are diffident in probability of causing protection misoperations; secondly, introducing an environmental factor and a power flow factor by a belief rule base, building a protective system markov model of considering the influences of the environment and system power flow, and organically combining the hidden failure probability model with the markov model, so as to build an accurate hidden failure model; and finally, building a risk evaluation method of considering cascading failures on this basis. According to the accurate hidden failure model-based cascading failure risk evaluation method for the power transmission system, analysis on risk evaluation of the power system can be effectively carried out.