Abstract:In the period of measuring multi-beam by using RTK technology, GPS elevation plays an important role in providing instantaneous vertical datum. During the actual operation process in the sea, GPS signals often happen the problem of out of lock. It will cause mutations of some epoch elevation data, and distortion of submarine topography. In this paper, setting Maoming project as an example, according to EGM2008 geoid model, by using elevation fitting method, in the process of measuring multibeam bathymetric, GPS ellipsoidal height will convert to normal height. Then pointing to the phenomenon of losing and locking GPS signals, the method of using elevation fixed solution to calculate sea tide surface by using RTK technology has been put forward. The advantages of this method have been explained as well.