Abstract: The closed-Brayton cycle has extensive application prospects in high-power space nuclear power. The performance of Brayton cycle could be improved with the helium and xenon mixture as cycle fluid and it could be directly used as the coolant of a reactor due to its good heat transfer performance. In concept design stage, the single channel program of helium and xenon mixture cooled reactor was developed with the need of frequent modification of reactor design. The properties of helium and xenon mixture were predicted with theoretical methods. The program was written in FORTRAN 90 with the plotting function integrated. This program can be used to calculate annular channel and circular channel. The results calculated by single channel were compared with those of FLUENT or experimental data for the same example, and it is verified that this program is correct.