The invention discloses a self-weighing device of an air suspension truck and a method thereof. The method comprises the following steps: collecting inner air pressure of air springs via a pressure sensor, converting the inner air pressure into analogue electrical signals, transmitting the analogue electrical signals to an analogue-to-digital converter connected with the pressure sensor, then carrying out data processing on digital signals subjected to analogue-to-digital conversion via an electronic control unit ECU, calculating corresponding vertical load applied to each group of air springs, carrying out summation calculation on the data so as to obtain sprung mass, and primarily calculating to obtain the total mass of the truck because unsprung mass is a constant value. In view of the system errors, compared with a fixed on-ground weigher, correction factors are introduced into the algorithm, so that the more accurate total mass can be obtained; a driver can more conveniently obtain the total weight of the truck in real time; the occurrence of overweight phenomenon is effectively controlled.