The invention provides an automatic transverse moving device of a heavy-load top door. The automatic transverse moving device is provided with two main body mechanisms, wherein the two same main body mechanisms are respectively fixedly arranged at the left end and the right end of a wind tunnel top door; the top door is connected with a support arm; the support arm is arranged at the upper end of a guide rail through a pulley; a servo motor is connected with a planetary gearbox and is then connected with a connecting base; the servo motor and the planetary gearbox are connected with a front support arm through the connecting base; a gear wheel is connected with the output end of the planetary gearbox; a rack is fixed on a pedestal; and the gear wheel and the rack are effectively engaged. According to the invention, an industrial control computer is internally provided with an operation interface and a motion control program, and motion control over the alternating-current servo motor is realized through a motion control board and an IO (Input Output) expansion board of the computer by utilizing a motion control function of the control board. According to the automatic transverse moving device, automatic transverse moving of the heavy-duty top door can be realized; and the automatic transverse moving device is stable, reliable and safe to operate.