To address the problem of reliability assessment accuracy of the electric-gas coupled systems, an electric-gas coupled system reliability assessment method considering multi-state equipment models and thermal inertia is proposed. Firstly, a multi-state model of the combined cooling, heating, and power (CCHP) equipment is established, including normal operation, power and heat supply, derated power supply and shutdown. Then, a minimum curtailment load model considering thermal inertia is established based on the multi-energy flow constraints. A reliability index is constructed based on the thermal comfort characteristics of the users, and the effectiveness and adaptability of the method are verified through a case study of a system containing a 33-node power supply, 32-node heat supply, and 11-node gas network based on a time series Monte Carlo simulation method.