The invention discloses a device of deeply treating oil sludge by a microwave and plasma technique. The device disclosed by the invention is a two-section compound structure: a microwave section and a plasma gasifying section. The upper end of the microwave section is connected with the feeding section, the lower end of the plasma gasifying section is connected with an ash collecting section, the lower end of the microwave section is connected with the upper end of the plasma gasifying section, the gas outlet is arranged below the plasma gasifying section and above the ash collecting section, and a gas product is extracted by a suction pump. A microwave generator is arranged on the inner side wall of the microwave section for heating, evaporating and cracking moisture and light components in the oil sludge. Plasma guns are symmetrically arranged on the inner side wall of the plasma gasifying section for gasifying slags and heavy components which are incomplete in reaction by the microwave section to obtain more combustible clean gases. The device disclosed by the invention can improve the problems of waste of petroleum resources and secondary pollution and the like caused by conventional oil sludge treatment methods. The energy loss is reduced while oil sludge is deeply treated.