Abstract: The sub-atmospheric heat exchanger is a key component of the superfluid helium cryogenic system. The purpose of this study is to design and optimize the plate heat exchanger and apply it to the liquid helium temperature zone. A heat transfer model of heat exchanger with variable physical parameters was established by the distributed parameter differential method. And a procedure for designing and checking the plate heat exchanger was developed based on this model. It takes thermal fluid outlet temperature, sub-atmospheric pressure drops and heat exchanger volume into consideration to achieve the optimized parameters of the herringbone corrugated plate. Multi-objective optimization is carried out by NSGA-Ⅱ and the selection of plate heat exchanger is completed on the premise of optimal heat exchanger volume. Three optimal design schemes were obtained and one of them is selected to produce the plate heat exchanger prototype. The reasons for the high design effectiveness of heat exchanger are explained by analyzing the variation of heat exchanger performance with the number of hot fluid flow channels.