Abstract: Based on the field data of velocity profile observed at 23 measuring points distributed over the Yangtze River estuary in March and September,1996,the momentum coefficients are calculated and their distribution characteristics are obtained through statistical calculations. For different typical time intervals and different places in the Yangtze River estuary,the results of linear regression show that the momentum coefficients are larger for flood than forebb,and for flood season than for dry sea son,that they increase from spring tide,mean tide to neap tide on temporal distribution,and that they increase from the out side of the month to inside the month for the North Branch,and increase at first and then decrease from outside the month to inside the month for the South Branch,the maximum value appearing near the month where riverflow crosses tide on spatial distribution Through analysis,the feature of frictional resistance in the motion of tide is better understood,and an easy approach is provided for choosing the Manning coefficient for numerical simulation of plane 2-D tidal current.