Abstract: Improving arc penetrability is of great importance in plasma arc welding. The experiment system of the new welding process, named plasma arc welding with additional focusing by metal powder, is designed and developed in this study, and the welding test is conducted. The data acquisition of electric signal, visible signal, and spectral signal is done during welding process. The weld formation, arc voltage, molten metal transfer, and arc spectrum are analyzed. Under the same welding current 195 A, comparing plasma arc welding with additional focusing by metal powder with traditional plasma arc welding, weld penetration increases 1.29 mm in value, and weld width decreases 1.65 mm in value, and arc voltage increases 0.63 V in value. Within the scope of 230 ~ 270 nm in wave length, characteristic spectral lines of element Fe and Cr during plasma arc welding with additional focusing by metal powder increase in quantity, compared with characteristic spectral lines during traditional plasma arc welding. It is found that, under the same welding current, arc penetrability in plasma arc welding with additional focusing by metal powder is bigger than that in traditional plasma arc welding.