Abstract: The feasibility of the stellar detection within the atmosphere in daytime by using light star sensor with small field was analyzed from the sky background, the spectral properties of star, and the structure characteristic of star sensor. Using the method of spectral filtering and reasonable choice of system parameters, a light star sensor was developed. Moreover, star detect experiment in daytime was carried out in high altitude area. With the observing altitude of 3 km, the atmosphere visibility of 10 km and the field of view of 21.5, the maximum detectable stellar magnitude limit was 3.8 when the avoiding angle of the sun was out of 30. The theory analysis and experiment result both indicate that light star sensor with small field can detect star in daytime.