Abstract: GPS phase delay contains a lot of information that can be used to obtain atmospheric parameters with certain methods. Based on ground-based GPS phase delay, a one-dimensional variational (1DVAR) assimilation algorithm combined with an empirical model is proposed to obtain the atmospheric refractive index. The assimilation experiment is carried out by using simulated GPS phase delay data, and also verified with actual measured data. The influence of the background error settings on the result of assimilation is discussed. The experimental result shows that the 1DVAR assimilation algorithm can get high-precision atmospheric refractive index in 0-60 km height. The background error settings of the lower layers can affect the assimilation result in the whole height range. The atmospheric refractive index obtained from the assimilation experiment is used to correct the radio wave refraction, and the result is very good, which can reach 1 mm scale correction accuracy.