Abstract: In this article the authors investigated some technical problems of unshielded magnetically impelled arc butt welding machine,such as power source,magnetic impelling unit,program control unit and welding parameter monitoring device.After analysing the unshielded MIAB welding process and the effect of welding parameters on welding quality,the authors established the formula for calculatirg the temperature field of abutting ends of workpieces and also the formula for setting optimum welding condition.An unshielded MIAB welding machine has been preproduced,featuring high efficiency,energy saving,and excellent quality of welded joints,It is best for production line application.