The invention provides a detection rule updating method and an electrical safety monitoring system. The method includes the following steps: each detection terminal detects fault information of an electrical line where the detection terminal is located according to stored detection rules, and sends the detected fault information to a server; the server receives the fault information, and sends overhaul requests to preset overhaul terminals; the overhaul terminals receive the overhaul requests and fault types input by overhaul personnel for the overhaul requests, and send overhaul results including the fault types and fault identification codes to the server; and the server receives the overhaul results, associates the fault information with the fault types in the overhaul results, analyzesthe fault information associated with each fault type to get the feature information of the fault type, and updates the detection rule for the fault type stored in each detection terminal according to the feature information. Thus, the inaccuracy of detection rules caused by the change of the power system can be avoided.