The utility model discloses a temperature/humidity monitoring alarm device for a cable trench of an unattended transformer substation. With the temperature/humidity monitoring alarm device of the utility model adopted, the problems existing in temperature/humidity monitoring and alarm of the unattended transformer substation can be solved, The temperature/humidity monitoring alarm device comprises the cable trench of the unattended transformer substation; a temperature sensor (1) and a humidity sensor (2) are arranged inside the cable trench; the temperature sensor (1) and the humidity sensor (2) are electrically connected with a local computer (4) respectively through a serial port circuit module (3); the local computer (4) is connected with a display (5) and a local wireless transmitting and receiving device (6); a remote computer (8) is connected with a remote transmitting and receiving (7); and the local computer (4) is electrically connected with the remote computer (8) through wireless signals. The temperature/humidity monitoring alarm device of the utility model provides a reliable basis for timely acquisition of temperature/humidity change situations inside the cable trench for operation and maintenance departments.