To reduce the thermal design errors of high-altitude optical remote sensor and improve the efficiency of its thermal control, the thermal design parameters of high-altitude optical remote sensor were analyzed using the method of sensitivity analysis. Based on the energy conservation law, the heat balance equation of optical remote sensor was built in the high altitude environment, and the sensitivity analysis of the thermal design parameters which could influence the temperature distribution of the lens assembly was achieved. The analysis results show that heat convection, internal heat source and the thermal resistance between components have great impact on the temperature difference of lens assembly in high-altitude optical remote sensor. The test results show that the thermal design based on the sensitivity analysis results is rational and effective.