Abstract: The orbital spacecraft is influenced by the space environment, which would cause the performance degradation of the spacecraft or its subsystems, even the mission failure. Therefore it is necessary to analyze and evaluate the space environmental effects, among which the primary concern is to determine the exposure flux of the space environmental factors. In this paper, the Monte-Carlo method is applied in the calculation of the exposure flux of the space environmental factors, such as the atomic oxygen, the micrometeoroid, the solar pressure, the atmospheric drag, the radiation dose, and the outgassing contamination. A general algorithm of calculating the exposure flux based on the Monte-Carlo ray tracing is proposed, and the calculation procedure is described. The new algorithm is verified through test cases. It is shown that the calculation results with the general algorithm are in good agreement with theoretical or reference values.