The invention discloses an emergency processing method of a transformer cooling box PLC fault, and a normally open relay. The emergency processing method comprises a cut-off automatic control module,and the working steps are as follows: setting relays K11 and K12 on a power line of a PLC output common end, connecting normally open contacts of K11 and K12 with a power supply of the PLC output common end, when the PLC is running normally, locating both K11 and K12 in a closed state, when the PLC is faulty, disconnecting both K11 and K12, and cutting off all automatic control loops, the problemof automatic, manual and emergency input of a cooler after the current PLC fault is solved by adding elements and devices and node loops thereof, the circuit is simple, the structure is simple, the emergency speed is high, the requirements of safe operation of a transformer are met, a reliable guarantee is provided for the safe operation of a power grid, and a sufficient preparation time is provided for PLC maintenance.