It was an important part of the intelligent substation to monitor the status of the substation equipment. A real-time on-line monitoring system based on image processing technique and photoelectric sensing technology of SF6 gas pressure was designed aimed at the characteristics of on-line monitoring of high voltage circuit breaker SF6 circuit breaker. This paper proposed a rapid alarm instrument image reading algorithm aimed at colored SF6 pressure gaugeused in substations. Image processing and identification of SF6 gas pressure were based on the algorithm.SF6 gas pressure state on-line monitoring data transferred through the ZigBee wireless communication technology.The SF6 gas pressure state online was displayed based on the background software written in LabVIEW . Preliminary laboratory tests were carried out to verify the feasibility of the system.