Position accuracy of star sensor is restricted by color temperature of star. In order to analyze the effect of color temperature in star sensor, the model of stellar spectrum was presented in this paper. And the position errors of star, which were caused by different stellar spectra, were calculated in an optical system of star sensor. The results show that the star position errors are not remarkable near the optical center. And the effect of color temperature could be minimized by reducing the working wavelength range of optical system, but the spot intensity would be lower at the same time. For example, if the working wavelength range is reduced from 300 ~1 100 nm to 400 ~800 nm, the single star position errors will be 0.042 2″、1.965 2″ and 3.389 1″ when the field view are (0°,0°), (0°,2°) and (0°,4°) correspondingly, which are about 54％、65％and 70％of the original errors. And the spot intensities are about 58％, 62％, 63％ and 51％ of the original when color temperatures of star are 9 600 K, 7 600 K, 5 600 K and 3 600 K correspondingly.