The optic system temperature distribution that is solved by finite element method with the software of I-DEAS ,that will descend the image quality in star sensor if it is not uniform. The effects of the outside and inside surface coat, the angle of sun incidence, the heat conduction of the drawtube and the thermal joint conduction on temperature distribution have been analyzed. It is shown that, the average temperature of system is decided by the outside and inside surface coat and the angle of sun incidence. The temperature difference is decided by the heat conduction of the drawtube and the thermal joint conduction. It is found that, when the ratio of absorptance and emittance of outside surface coat change from 0.25 to 4, the average temperature is from -78.10 ℃ to 66.53 ℃. When the emissivity of inside surface coat change from 0.2 to 1, the average temperature is from 25.00 ℃ to 18.22 ℃. When the angle of sun incidence change from -60° to 0°, the average temperature is from -9.59 ℃ to 18.22 ℃. When the drawtube is the alloy of titanium or aluminum, the temperature difference is 6.85 ℃ and 0.31 ℃. When the thermal conductivity of the thermal joint conduction is 237 W/(m·k), the temperature difference is 2.37 ℃. The conclusion has great c significance to the engineering.