Abstract: The thermal insulating board inside the space camera acts as a role of insulating the internal optic structure from the sunlight radiation which can cause a sharp temperature rise of the board, since it is usually thin and does not add extra cooling components. The difference of increased temperatures on the insulating board can increase interior infrared stray radiance. A full set of thickness optimization method for thermal insulating board was presented. Using the mechanism of bionic optimization, the thickness of the insulating board was optimized according to the temperature gradient difference along the board while keeping the total volume unchanged. Then the Gauss filtering was conducted to make the thickness of insulating board change smoothly and easily for manufacturing. Through comparing the temperature profile and infrared radiance before and after optimization, the result showed that the highest temperature reduced by 3.8℃, and the infrared radiance at the wavelength of 3 m~5 m and 8 m~12 m reduced by 15%. The optimized method could be used to reduce the interior stray radiance by combining with other methods.