Abstract: Plasma electrolytic deposition (PED) is a new technology in surfaceengineering. The paper introduces the main mechanism of PED, as well asitsapplications in different fields such as surface modification of metal,electronic films, medicine films, DLC films and nitrogen-containing carbonfilms etc. The principal mechanism of PED is as follows: when the electrical potentialbetween the anodic and cathode reaches a certain value, the electricalfield strength in the electrode/ electrolyte interface is sufficient toproduce a dielectric breakdown, which is utilized to deposit ceramic layer orto saturate some elements into the substrate. As its applications to thestructuralmaterials, PED is successful in increasing material's anti wearand anti corrosion ability by depositing ceramic layers to light metals suchas aluminum alloy, magnesium alloy and titanium alloy or saturating carbon,nitrogen into steel. Electrolyte containing calcium and phosphorus isutilized to deposit bioactive film on the surface of titanium alloy to formchemical bond with host bone. Appropriate electrolytes are chosen tosynthesize perovskite type electric films such asBaTiO$_{3}$、SrTiO$_{3}$、NaTaO$_3$、SrZrO$_3$ etc. High voltageelectrolysis of organic liquid is utilized to form high performance filmssuch as DLC films and carbon nitride films. The toughening mechanismand some important mechanics problem about PED coatings such as theinfluences of micro defects on macro performance, interface fracturetoughness, residual stress and adhesion strength are discussed and needfurther research work. Ceramic coating deposited with PED on aluminum alloy hasbeen used successfully. Furthermore, PED is also suitable for surfacetreatment for steel, biological active materials and electronic films.