As the power system develops towards one with high penetration of renewable energy, the system flexible resources are seriously insufficient. It is urgent to guide the controllable resources of end-users to actively participate in the balance regulation service. This paper proposes a multi-stage electricity market clearing framework for day-ahead energy market, day-ahead reserve market and real-time balanced market, where load aggregators can aggregate end-users to join in the multi-stage coupled markets. In the day-ahead energy market and reserve market, the state perception model for flexible sources of load aggregators is established. Also, the bidding model of load aggregator and the market clearing model of system operator for the day-ahead energy and reserve market are put forward. In the real-time balanced market, a bidding model of load aggregator based on the surplus flexible resources of end-users is proposed. The system operator clears the real-time balance market and dispatches the collected flexible resources based on the actual system supply-demand demand. A modified IEEE 30 bus system is used to test the proposed market framework. The simulation results show that the proposed framework can effectively stimulate end-users to actively respond to the system operation demand, and to reduce the risk of system supply and demand imbalance. This work is supported by the Science and Technology of State Grid Corporation of China (No. SGNWO000DKJ S2100269).