Evaporation method has been widely used in radioactivity wastewater treatment of nuclear power plants because of its high decontamination factor (DF) and wide application range of water quality. However, the traditional evaporation system has high energy consumption. Aiming at the recovery of latent heat of secondary steam during stable evaporation of wastewater in radioactivity, a new evaporation system & mechanical vapor recompression (MVR) was proposed and studied. Firstly, a mathematical model is established according to the conservation equations of mass and energy. The factors affecting energy consumption, decontamination factors, and secondary waste that needing attention due to radioactivity are discussed. According to the improved scheme, a prototype was built and the wastewater treatment experiment in simulated radioactive water was carried out. The actual energy saving rate and decontamination factor are calculated and analyzed. The results show that, at the conditions of evaporation rate of 600kg/h and evaporation temperature of 100°C, compared with traditional evaporation, MVR can save 84.8%energy, and the decontamination factor (DF) reaches 105 in simulated waste liquid treatment experiment. MVR shows that this method has obvious advantages in economic and environmental benefits.