In order to determine the optimal break point sets（OBPSs） for protection coordination in multi-loop network， four indices are introduced as the judgment criterion of OBPSs， the math model looking for OBPSs is developed. Then， based on the principle of bacterial colony chemotaxis algorithm， a new method of determining OBPSs is presented. Comparing with the existing method， the proposed method can find the optimal minimum break point set. An example analysis proves that this method is valid and applicable.