Medium-thick 16MnR steel plate has the advantages of high strength and good plastic,and is commonly used for the special manufacture of storage container for nuclear waste. However,there are some disadvantages of welding the medium-thick 16MnR steel plate by using the traditional root welding procedure with backing plate, including low efficiency,complicated process and instable quality of appearance of weld. Based on this problem,the plasma arc welding and low/high frequency pulse TIG welding are used to realize double-sided forming of single-sided welding of 16MnR steel plate without backing plate. The experimental research shows that the double-sided forming of single-sided welding with 8 mm thick blunt edge can be realized by the wire-filling plasma welding procedure,and the defect-free appearance of weld is obtained,but its parameter adjustment interval is narrow,the welding process is tend to lose stability when facing small fluctuation in the production process;When using low-frequency pulsed DC TIG welding,the full penetration of the 5 mm thick blunt edge can be stably realized,the front surface of the weld shows fish scale pattern with a large gap,and the weld heat affected zone has more lath martensites,which increases the strength and toughness of weld. When using high-frequency pulsed DC TIG welding,the welding heat input reduces,the arc obviously shrinks,and the penetration increases,the maximum penetration of 7 mm can be welded. With the stable welding process and high welding efficiency,there are many wedmanstatten structures in the weld zone and the fusion zone,and numbers of lower bainite structure with better toughness at low temperature in the heat affected zone.