The invention relates to a main transformer air cooling system secondary loop circuit control device and an air cooling control system. The main transformer air cooling system secondary loop circuit control device comprises a conversion unit, a first on-off control unit, a first time delay control unit, a second on-off control unit, a second time delay control unit and a two-way control unit, wherein the conversion unit is connected with a current in-use power source and a standby power source. Via the main transformer air cooling system secondary loop circuit control device and the air cooling control system, double power source switching reliability can be improved and alarm signals can be optimized when wire coil breakage is caused due to long-term electrification of a relay wire coil. Via the main transformer air cooling system secondary loop circuit control device and the air cooling control system, any one of the two power sources can be chosen as a main supply power source via a conversion switch in actual application while the other one can be used as the standby power source; after switch to the standby power source from the main supply power source due to faults of the main supply power source, no automatic return to the main supply power source (automatic switch instead of automatic return can be achieved) is conducted when the faults of the main supply power source are not checked; switch back to a malfunctioning power source and repeated switch can be prevented.