The invention discloses a diesel engine air valve calibration device and a calibration method thereof. The device is mainly composed of an air valve clearance pressure sensing device and an adjustingscrew adjusting and fixing device. The air valve clearance pressure sensing device comprises an ampere meter, a power supply, a first force sensing resistor and a second force sensing resistor. The thickness of the first force sensing resistor is the same as the air inlet valve clearance. The thickness of the second force sensing resistor is the same as the exhaust valve clearance. The adjusting screw adjusting and fixing device comprises a transverse sliding block, an adjusting device, a support fixing device and a support. The method comprises the steps of placing the force sensing resistorsinto the air valve clearances to be adjusted and converting the pressure between the air valve clearances into current changes of the ampere meter so as to avoid errors generated in the process of artificially sensing the pressure; adjusting and fixing the air valve clearances through the adjusting screw adjusting and fixing device to avoid the situation that a screwdriver is held with the hand and the fixing moment is insufficient and repeated adjustment is avoided. Through the diesel engine air valve calibration device and the calibration method thereof, the air valve clearances can be adjusted more accurately, time can be saved, the labor amount can be reduced, and the requirements for the technical level of staff can be reduced.