Abstract: Considering the multiple time scales of integrated energy system（IES）,thermal inertia of thermal subsystem and basic operation strategies complementary multiple energy,a method of reliability evaluation for IES is proposed.Firstly,in order to calculate the support capacity of each subsystem in different time intervals and the index of reliability gain for complementary multiple energy,characteristics of complementary multiple energy for IES are discussed based on the energy hub model.Then,the thermal inertia is modeled in quasi-steady state.The exergy difference and specific features of different energy are described by energy analysis,and the system basic operation strategy is set.Finally,the reliability of IES is calculated by Monte Carlo method based on Markov chain.The simulation results of a user-level for IES in Germany show that,when the energy flow input of a subsystem is insufficient,mutual operation will bring greater reliability gain,and the current reliability evaluation method without considering thermal inertia is conservative.