Abstract: Time delay between GPS system and MBS is found in precise multibeam surveying.We present two kinds of methods for the determination of the time delay.One is the position match;the other is the consistent vertical motion method.For the first method,time delay is determined and calculated by comparing corresponding position in NMEA-0183 file telegram and NAV file formed by MBS for navigation in MBS surveying.For the latter,based on the vertical motion consistency in monitoring vessel motion,time delay is determined by the quality control of original data,altitude correction and the determination of maximum comparability of two vertical motion waves.The two methods were tested by a few experiments and proved to be accurate and credible in the determination of time delay.