Abstract: To achieve online monitoring of oil leakage status of oil filling equipment in substations, this paper designs and develops an online monitoring system for oil filling equipment leakage in substations based on trusted WLAN wireless access technology. The system mainly consists of three parts: drip rate monitoring module, alarm module, and other related modules. The function of the drip speed monitoring module is to achieve the counting and timing of oil droplets, the function of the alarm module is to remind the centralized control operators of abnormal oil droplet leakage monitoring, and other related modules are to support the operation of the monitoring system. Finally, system testing and experimentation were conducted in a certain substation, and the results showed that online monitoring of oil filling equipment can be achieved, meeting the requirement of timely detection of defects from general to severe.