The invention discloses an industrial mechanical arm machining unqualified product counting device and method based on construction synchronization. The device comprises a base plate and a transversebeam, a controller is arranged on the base plate, a motor is arranged beside the controller, a protection shell is arranged on the exterior of the motor, a control panel is arranged on the side face of the protection shell, a bearing seat is arranged beside the motor, a first hydraulic rod is arranged above the bearing block, a first distance measuring probe is arranged on the side wall of the first hydraulic rod, the transverse beam is arranged at the top of the first hydraulic rod, a moment detecting device is arranged inside the transverse beam, a back beam is arranged at the back end of the transverse beam, a guide rail groove is formed in the back beam, a movable base is arranged on the guide rail groove, a second distance measuring probe is arranged above the movable base, and a balancing weight is arranged below the movable base. The industrial mechanical arm machining unqualified product counting device and method have the beneficial effects that unqualified products can be identified through detection on key part sizes and weights of parts, and the detection efficiency is improved.