Abstract: In order to provide parameters design method of airborne all-day star sensor, in this paper, the SNR(Signal to Noise Ratio) computation formula for star targets detection was derived according to the SNR formula of optical-electric detection system and sky radiance data from Modtran software. The relation between detection SNR and diameter, F number,exposure time was researched for the stars of visual magnitude of 3.5,4,4.5, and the corresponding parameters design method of airborne all-day star sensor was given. In order to verify the correctness of the design method, the ground-based observation test was carried out. Polaris(Mv2.02) was selected as target, and the all-day star sensor prototype with 83 mm diameter, 1 500 mm focal length was designed. Through the ground-based observation test, at the most powerful sky radiation moment the SNR for detection Polaris was 6.84 dB, met the minimum detection requirements 6 dB from the theoretical calculation. The correctness of the design method is verified.