The invention discloses a device for automatically welding a spiral tubular pile. The device is characterized by comprising a rotating frame, a guiding support, a limiting stopper, a welding gun frame and a guide rail, wherein the rotating frame consists of a lathe bed, a gearbox and a tailstock; the gearbox is fixed together with one end of the lathe bed; the tailstock is arranged on the lathe bed; the guiding support is fixed on the lathe bed; the guide rail is fixed on the guiding support; a vertical column of the welding gun frame is arranged vertically; and one end of the vertical column is connected to the inside of the guide rail, and the other end of the vertical column is connected with the limiting stopper. According to the device, spiral motion of a welding seam is decomposed into uniform circular motion and uniform linear motion; the rotating frame drives the spiral tubular pile to do the uniform circular motion, and the limiting stopper is attached to the guide rail and makes a positioning wheel pressed against a spiral blade to do the uniform linear motion so as to finish composite motion of the welding seam; and the device has the advantages of simple structure, accurate blocking process, high welding continuity, high quality of the welding seam and high working efficiency.