Plasma electrolytic saturation technology on surface of metals includes plasma electrolytic carburizing, nitriding, boriding, etc. The technology takes advantages such as high processing efficiency, low applied voltage, simple treatment process and low cost. Here, the latest development of plasma electrolytic boriding (PEB) on the surface of steel, titanium and other metals was introduced. The discharge process and basic principle of PEB were analyzed. The optical emission spectrum in boriding process was detected, and the characteristic parameters of electron temperature and electron concentration in plasma discharge region were evaluated. The growth process and formation mechanism of boride layer were analyzed. The effects of some key parameters such as composition of metal substrate, applied voltage, treating temperature and electrolyte composition on micro-structure and phase constituents of the boride layers were discussed. Finally, some unsolved problems and the future trends of plasma electrolytic boriding technology are discussed and prospected.