The utility model relates to a device for testing the running axle load of a passenger car, comprising a resistance strain sensor, an A/D (analog-to-digital) transducer, a microprogrammed control unit circuit, a display, an alarm and a power supply. The resistance strain sensor is fixedly arranged on a front-rear axle cross member of a truck, and is connected with the microprogrammed control unit circuit through the A/D transducer; the output of the microprogrammed control unit circuit is connected with the display and the alarm; the display can be arranged independently at the mounting position, and alternatively, is arranged at a position seen by the truck driver from an instrumentation board. The device can display the carrying capacity of the car, and therefore the driver knows the detailed data of the carrying capacity of the car and pays attention to the reliable running of the car; traffic polices can inspect the overload situation through the device to eliminate overload potential hazards, so that the running safety of the passenger car and the ride comfort of passengers are improved; and the device is suitable for trucks as well as large-sized passenger cars.