Disclosed is an integrated energy system operational optimization method considering thermal inertia of district heating networks and buildings, comprising the following steps. Step 10: respectively establish a district heating network model considering transmission delay and heat loss and a building model considering thermal storage capacity. Step 20: establish an integrated energy system optimization model consisting of a combined cooling, heat and power system model, the district heating network model and the building model. Step 30: solve the integrated energy system optimization model to obtain an optimal scheduling plan, control outputs of a gas turbine and a gas boiler per hour according to the optimal scheduling plan, and purchase electricity from a power grid and a wind power. According to the method, both the district heating network and buildings are included in a scheduling scope, so that the load adjustment with multiple degrees of freedom can be achieved.