In order to explore the condensation heat transfer performance of the mixed working fluid in the rectangular spiral tube heat exchanger, a numerical model of condensate heat transfer with non-condensable gas in the rectangular cross-section spiral tube was established, and the condensation heat transfer characteristics and flow characteristics of the mixed working fluid under the design conditions, as well as the influence of the proportion of non-condensable gas components and the aspect ratio of the model structure on it were discussed. The simulation results show that the heat flux density of the spiral tube decreases first and then increases under the influence of centrifugal force. In the late stage of condensation, condensate forms annular flow and plunger flow, which effectively enhances the heat exchange performance of exhausted gas in the channel and the outer wall. The larger the proportion of non-condensable gas components, the stronger the inhibition effect of heat flux density in the condensation stage of the spiral tube, and the worse the heat exchange effect. When the width-to-height ratio of the channel is greater than 1, the secondary flow intensity in the spiral tube channel is larger, and the heat exchange effect of exhaust gas is better.