The invention discloses an Internet-of-Things-technology-based transformer substation cable trench environment state monitoring system and monitoring method. The system comprises an intelligent cabletrench data acquisition system, a communication network system, an alarm system, a concentrator and a background monitoring system. Environmental data, detected by the intelligent cable trench data acquisition system, in a cable trench are transmitted to the concentrator through the communication network system; the concentrator controls the alarm system to send out an alarm signal; the concentrator communicates with the background monitoring system to realize remote transmission of data and receiving of a remote control instruction. Since operation environment data such as the temperature, humidity, water level, harmful gas concentration and the like in the cable trench are monitored in real time, once any abnormal phenomenon is monitored, an alarm signal is generated and the alarm information is pushed to all the monitoring and maintenance staff members actively in real time, so that early warning is performed in advance once any abnormity occurs and thus the accident can be eliminated from an unburned situation.