Abstract: The phase time-differential method, which is based on the phase rate observation to calculate the carrier velocity, is easily influenced by the cycle slips errors in carry phase observations. The widely used cycle slips processing method can correct the slips errors which are greater than 1 cycle, however there is not any easy and convenient method that can correctly solve the problems when slips are smaller than 1cycle. Through analyzing, this kind of error can lead to the accuracy magnitude of calculated velocity down to dm/s, the influence should be corrected in high accuracy velocity calculating application. Aiming at the characteristic of the phase rate observation, this paper calculated the carrier velocity by using the robust least square estimation, choosing the equivalent weight by IGGⅢ principle to lower the contribution of the observation that contain the gross error which is smaller than 1 cycle. By Calculating and analyzing the data acquired from a experiment of aviation flying, the result shows that the accuracy magnitude of velocity can keep on after RLS estimation.