For the thermal analysis of equipment installed on the international space station (the ISS equipment), this paper uses formulas of external heat flux of simplified hexahedral spacecraft in the low earth orbit to calculate the external heat flux of the ISS, and analyzes the variation characteristics of the external heat flux of the ISS with orbital parameters. Based on the AMS heat flux model, the Alpha Magnetic Spectrometer (AMS) is used as an example of the ISS equipment to analyze the impacting factors of external heat flux of the ISS equipment. The results show that the external heat flux of the AMS varies with the solar beta angle and the angular distance between the ISS and Sun-ISS junction. For different solar beta angles, the thermal effect by the fixed parts of the ISS on the AMS is stable. Operations of the ISS port solar arrays, the main starboard radiator can change the external heat flux of the AMS. The variation of external heat flux of the AMS with the ISS normal flight attitude is different from the circumstance with ISS slide flight attitude. Therefore, the major impacting factors of the external heat flux of the ISS equipment are the solar beta angle, the angular distance between the ISS and the solar-ISS junction, the ISS configurations and the ISS operations.