The utility model discloses a dc -to -ac converter that promptly ventilates detects control box, including detecting the control box main part, the state indicating circuit that detects the dc -to -ac converter power supply circuit that is provided with control box power supply circuit in the control box main part, is connected with dc -to -ac converter power input end, be connected with dc -to -ac converter running state output, hold detection circuitry and the expert fan drive circuit who is connected with dc -to -ac converter power output. The utility model discloses can promptly ventilate the dc -to -ac converter at the ferroelectric passenger train in ground and damage the back, detect it fast on the spot, and can show dc -to -ac converter " RUN " operation ", " FAULT " output signal such as " troubles ", but also can connect the ventilation blower, demonstration promptly ventilate inverter output voltage and frequency.