By supposing the atmosphere is of spherical symmetry,starlight refraction model is given deriving from atmospheric refractive index, refractive path in atmosphere and Snell law for the observing method by large field of view star sensors in autonomous orbit determination. On the assumption that the starlight refraction does not happen on the spherical surface whose altitude is larger than 60 km, the relations among the elevation angle θ60 of starlight on atmospheric altitude of 60 km, the starlight refraction angle γ and the starlight tangent altitude h are obtained. And the result shows that range of change of θ60 is from 0°to 7°. At last, the orbit determination simulation is done using this refraction model, and the validity of the model is shown.