Abstract: Helium purification and helium auxiliary system is one of important systems guaranteeing the safe operation of high-temperature gas-cooled reactor. Wire mesh mist eliminator in this system is one of the key components. It is used to separate waste water containing tritium, and remove moisture after reactor accident. Base on the ideal fluid model and packing pad model developed by Carpenter, a calculation model was presented for separation efficiency of mist eliminator. The calculation program SEP-WMME was developed based on the model. The calculation results fit well with experiment results. Theoretic analysis was carried out for the mist eliminator of regeneration system in HTR-PM helium purification system engineering validation test loop. The analysis results show that the inlet velocity is an important parameter for mist eliminator in regeneration system. When the inlet velocity is above 3.0 m/s, high separation efficiency will be obtained. The number of wire mesh layers also affects the separation efficiency remarkably. When the number of layers increases further to some extent, the separation efficiency increase becomes insignificant. The number of layers should be chosen properly by considering pressure loss. Additionally, the diameter of wire is an important parameter related to separation efficiency. The separation efficiency increases with the decrease of the wire diameter. The analysis is significant for structure design, optimization and safe operation of mist eliminator in helium purification and helium auxiliary system.