This paper presents a new method to identify switch information using the discrete bacterial colony chemotaxis（BCC）algorithm. Firstly， a mathematical model is developed for topology analysis and creation of measurement as well as DC flow calculation based on defined discrete variable information about the switch. Secondly， an evaluation index related to the discrete variables of switch information is given in the light of the measurement matrix and the results of DC flow calculation. Finally， an optimization method based on the improved discrete and update mechanism is presented. This method can quickly identify and modify the switch information to guarantee the accuracy of state estimation results. The feasibility of the algorithm proposed is proved by simulation results on an IEEE 39-bus system.