To investigate the thermal behaviour of electronic units of Alpha Magnetic Spectrometer 02 (AMS-02) in a simulated thermal-vacuum space environment, the integrated model of AMS-02 was programmed using the lumped parameter for AMS-02 and the shroud of Large Space Simulator (LSS). The Monte Carlo algorithm was used to calculate the radiative heat flux between AMS-02 and the shroud of Large Space Simulator. The heat transfer performances of heat pipes mounted in the main radiators of AMS-02 were entirely investigated under different gravity level using the integrated model. The maximum temperature difference of electronics mounted on AMS-02 is -31.1 ℃ for heat pipes operated under 0g and 1g gravity environments. Based on these calculations, the testing orientation to keep the normal performance of electronic units of the AMS-02 thermal vacuum and thermal balance (TV-TB) test is defined to be carried out in horizontal direction.