Abstract: In order to effectively identify the key business system and assess its security risk on the business process, a key business system identification model was proposed. Firstly, the evaluation attribute matrix and the system association degree matrix were obtained through establishing the business process correlation model. Secondly, the weighting method and relative proximity calculation method in the technique for order preference by similarity to an ideal solution (TOPSIS) were improved, and an improved TOPSIS method was used to identify the key business system. Finally, the entire business process loss was evaluated when information security incidents occurred in the business system. Experimental results show that the model can identify the key business system accurately and evaluate the business system impact on the entire business process effectively.