Tropospheric slant delay is one of the most significant error sources in navigation satellite systems. Its obvious randomness is mainly attributed to meteo-rological parameters (temperature, pressure and water vapor pressure, etc.). Aiming at the poor performance of tradition Tropospheric models, and the restrictions of radiosonde data in ray tracing, an improved method based on ray tracing is proposed. In this method, refractive index is improved by inserting in global grid of meteorological parameters, which get rid of the restrictions of radiosonde data. Meteorological data from Tsukuba(TSKB) stations in Japan are analyzed based on ray tracing technology and tradition models like Hopfield and Saastamoinen. Slant delay for 15 directions, from the zenith to 4° elevation, were computed. The results were compared with ray-tracing tropospheric slant delays from nearby radiosonde measurements, which demonstrate that the accuracy and stability of improved ray tracing method is superior to tradition models. The method can precisely provide the tropospheric slant delay in the circumstances where measured meteorological data are absent, so it is of practical engineering significance.