Load aggregator (LA) can supply system reserve by aggregating middle and small demand-side response resources. This paper discusses the contents of different types of interruptible load constract between LA and users based on different load characteristics of users. The operation modes of LA are presented, including the compensation scheme for interruption, prophase subsidy for users and participating in system supply-demand balance. The cost-benefit models of user, LA and power system are established, and the interaction between them is analyzed. Finally, based on the cases,the characteristics of different cost-benefit perspectives are analyzed, and the coordination of extra subsidy on each cost-benefit, the effect of compensation scheme on LA cost-benefit and the effect of participating in system supply-demand balance on each side are demonstrated. Some suggestions on implementing the program are given.