Abstract:High-rate GPS receivers are popular in real-time dynamic monitoring, but the multi-path effect is one of the key obstacles that restricts its development. However, a sidereal filter can eliminate this effect and improve positioning accuracy. The sidereal filter requires the preset time of each satellite compared to the day before. In this research, 8 526 days broadcast ephemerides are used to calculate the preset time. The Fourier series of 8 orders trigonometric functions is used to fit the series of the preset time. It shows a simple and effective way to estimate the preset time, instead of a more complex calculation. Using this method, the root mean square values of the residual coordinate sequences of N, E and U directions are reduced, and the ability of extracting deformation information is improved.This method therefore can be applied in engineering dynamic deformation monitoring.