The invention relates to a loading and unloading device of a work-piece. An automatic loading and unloading mechanical arm is composed of a positioning portion, a clamping portion and an inverting portion, wherein the clamping portion is connected with a sliding driver which is fixedly connected with an inverting mechanism, the inverting mechanism is in limited connection with a slider of a positioning mechanism, the slider is glidingly arranged on a guide track and is fixedly connected with a piston rod of a positional cylinder, and the positional cylinder and the guide track are respectively fixed on a top board. The invention employs the pneumatic control technique as a control and actuating mechanism which substitutes systems, such as an expensive numeric control servomotor and the like. Air is a medium of an air control mechanism. The invention has the characteristics of convenient using and maintenance, safety, reliability, low costs, long service life and the like. The invention has the advantages of wide adaptive range and low costs, and is capable of realizing the function of modularization and increasing the availability ratio of devices, being adaptable for wide promotion in market.