Due to poor economy caused by higher traditional reserve configuration, an economic dispatch model of reserve coordination at contingency state considering inverse-time characteristic of line protection is presented. The model aims to minimize the cost of generation and reserve under satisfying constraints of general unit and network security and combing with the inverse-time characteristic of line protection, relaxing general power flow constraints to thermal stability limit value of corresponding time scale according to reserve response time, then synthetically solve coordinated optimal reserve dispatch of different response speed to improve the economy of reserve configuration. The model is a mixed-integer linear programming problem, it needs to be linearized or nearly linearized in the model, and the commercial mixed-integer linear programming CPLEX solver is used to solve the problem. Finally, numerical experiences prove the rationality of the presented model and the effectiveness of the proposed approach in IEEE 30 systems. This work is supported by National Natural Science Foundation of China (No. 51677020), Sichuan Province Key Laboratory of Power Electronic Energy-Saving Technologies & Equipment (No. szjj2014-015), and Graduate Student Innovation Fund of Xihua University (No. ycjj2016159).