The closed-cycle Brayton gas-cooled stack with helium–xenon gas mixture as coolant has good prospects for application in deep space exploration. The printed circuit plate heat exchanger (PCHE) with compact structure, high pressure resistance and excellent heat transfer performance is a promising choice for high temperature recuperator of helium–xenon gas system. In this paper, a single rectangular channel model of the thermal pipe section of PCHE is established. The flow heat transfer characteristics of He–Xe in the PCHE high temperature rectangular channel and PCHE unit heat exchanger are investigated by using numerical calculation simulation software. For the development of the turbulence model of the helium–xenon gas mixture, the standard k-epsilon model using Kays’ empirical formula to modify Pr is chosen as the numerical calculation model. Numerical simulations of the PCHE heat transfer unit at rated operating conditions were carried out. And the effects of helium molar share are investigated. When the helium molar share increases to 92%, the flow velocity of the mixture gas can reach up to 16 m/s, and the pressure drop and heat transfer coefficient increases dramatically.