In the previous process for the regeneration of molecular sieve bed of helium purification system, there was only one closed loop included, which mainly consisted in sequence of diaphragm compressor, electric heater, molecular sieve bed of helium purification system, water cooler and water separator. The water partial pressure of circulating gas can only be reduced to the value equal to the vapor pressure corresponding to the operation temperature of water separator of helium purification regeneration system. For instance, if the operation temperature of water separator of helium purification regeneration system is 10 °C, the water partial pressure of process gas can only be decreased to 1227 Pa which is not low enough for the water adsorbed in molecular sieve bed to be desorbed at regeneration temperature of 250 °C. In addition, the regeneration temperature of molecular sieve bed of helium purification system only reached 200 °C in the past operation, which further made regeneration condition worse. In fact, the past regeneration process of molecular sieve bed led to an average distribution of water in the whole molecular sieve bed. And in the following vacuum degassing process of molecular sieve bed, tritium-containing waste water was partly emitted to the environment. As a result, no tritium-containing waste water could be collected in the water separator of helium purification regeneration system.