In addition to its capability to remove water, gas and impurities in oil like the functions of ordinary vacuum purifier, the purifier can also recover the inferior insulation oil, which could effectively remove the intensive oxide and free carbon, thus resumes antioxidation and acid/alkali water solubility characteristics. After treatment, the oil can meet the national standard in respect of water content, withstand value, gas content, acid value and medium consumption requirement. The purifier has multi-purpose functions. Its function of removal of water, gas or impurities and the regeneration system can operate separately and independently. They can also operate together at the same time, being easy to operate with higher effectiveness.