Abstract: In terms of the vertical position reduction for high-precision positioning in hydrographic survey,the heave factor is studied in this paper.Based on the differences between measured heave and total heave,the induced heave model is proposed.Then,with the RTK height and attitude data,both the accuracy of induced heave estimated by this model and the effect on those are presented.Numerical results indicate that the values of induced heave can achieve the decimeter level,which can influence the instantaneous height of the positioning center.The accuracy of induced heave and total heave can be higher by improving the accuracy of the positioning center offset measured,which is more important than those of roll and pitch measured.