The utility model relates to a relay protection secondary circuit state monitoring system, include: IR temperature transducer, humidity transducer, AD converter, singlechip, RS485 communication unit,concentrator singlechip, transformer substation's server. IR temperature transducer, humidity transducer pass through AD converter and singlechip and link to each other, and the singlechip passes through the RS485 communication unit with the concentrator singlechip and links to each other, and the concentrator singlechip passes through serial port communication and links to each other with the transformer substation server. The utility model discloses a IR temperature transducer and high accuracy humidity transducer can carry out secondary circuit environment real -time supervision to readingsecondary circuit through transformer substation relay protection information system and moving alarm information, the monitoring data source is comprehensive, can in time discover the secondary circuit abnormal operation situation, takes measures to improve, ensures the reliability of relay protection action.