Abstract: In this paper, a method of re-calibration for roll bias of multi-beam sounding system is proposed to solve the faltiness of multi-beam sunding transducer calibration. Based on the sounding data of smooth terrain, the roll bias angle of transducer, the dip of terrain, can be calculated by using the method of weighted least squares. The obtained bias angle can be used for roll bias correction of transducer in vessel model. The conclusion shows that the corrected bathymetry data in the overlapping area of adjacent two swaths is more consistent than before, the accuracy of multi-beam bathymetry data has been significantly improved.