An apparatus for detecting air tightness, having an air inlet end, an inflating end for an object to be tested and a standard part inflating end, the apparatus comprising: a pressure regulating component, wherein a first end of the pressure regulating component is connected to the air inlet end; a main isolating valve, wherein a first end of the main isolating valve is connected to a second end of the pressure regulating component, and a second end of the main isolating valve is connected to the inflating end for the object to be tested; a first bypass isolating valve, wherein a first end of the first bypass isolating valve is connected to a gas pipeline that is between the second end of the pressure regulating component and the first end of the main isolating valve, and a second end of the first bypass isolating valve is connected to the standard part inflating end; a second bypass isolating valve, wherein a first end of the second bypass isolating valve is connected to a gas pipeline that is between the second end of the main isolating valve and the inflating end for the object to be tested; a third bypass isolating valve, wherein a first end of the third bypass isolating valve is connected to a gas pipeline that is between the second end of the first bypass isolating valve and the standard part inflating end; a first high air pressure sensor, wherein a detecting end of the first high air pressure sensor is connected to a gas pipeline that is between the second end of the pressure regulating component, the first end of the main isolating valve and the first end of the first bypass isolating valve; a second high air pressure sensor, wherein a detecting end of the second high air pressure sensor is connected to a gas pipeline that is between the second end of the main isolating valve, the inflating end for the object to be tested and the first end of the second bypass isolating valve; a low air pressure sensor, wherein a detecting end of the low air pressure sensor is connected to a gas pipeline that is between the second end of the first bypass isolating valve, the standard part inflating end and the first end of the third bypass isolating valve; and a differential pressure sensor, wherein a first detecting end of the differential pressure sensor is connected to a second end of the second bypass isolating valve, and a second detecting end of the differential pressure sensor is connected to a second end of the third bypass isolating valve. a pressure regulating component, wherein a first end of the pressure regulating component is connected to the air inlet end; a main isolating valve, wherein a first end of the main isolating valve is connected to a second end of the pressure regulating component, and a second end of the main isolating valve is connected to the inflating end for the object to be tested; a first bypass isolating valve, wherein a first end of the first bypass isolating valve is connected to a gas pipeline that is between the second end of the pressure regulating component and the first end of the main isolating valve, and a second end of the first bypass isolating valve is connected to the standard part inflating end; a second bypass isolating valve, wherein a first end of the second bypass isolating valve is connected to a gas pipeline that is between the second end of the main isolating valve and the inflating end for the object to be tested; a third bypass isolating valve, wherein a first end of the third bypass isolating valve is connected to a gas pipeline that is between the second end of the first bypass isolating valve and the standard part inflating end; a first high air pressure sensor, wherein a detecting end of the first high air pressure sensor is connected to a gas pipeline that is between the second end of the pressure regulating component, the first end of the main isolating valve and the first end of the first bypass isolating valve; a second high air pressure sensor, wherein a detecting end of the second high air pressure sensor is connected to a gas pipeline that is between the second end of the main isolating valve, the inflating end for the object to be tested and the first end of the second bypass isolating valve; a low air pressure sensor, wherein a detecting end of the low air pressure sensor is connected to a gas pipeline that is between the second end of the first bypass isolating valve, the standard part inflating end and the first end of the third bypass isolating valve; and a differential pressure sensor, wherein a first detecting end of the differential pressure sensor is connected to a second end of the second bypass isolating valve, and a second detecting end of the differential pressure sensor is connected to a second end of the third bypass isolating valve.