Abstract: Based on the measured data of Xiaoshan to Yangtze Estuary reach, the temporal and spatial distribution law of momentum coefficients was studied. Then the difference of coefficients in beaches and deep trough was obtained and the empirical curve was established. The results showed that the momentum coefficients in wet seasons were higher than that in dry seasons in the estuary, while the law was totally contrary in the North Passage. The coefficients in spring tidal were higher than those in neap tidal from Xiaoshan to Shihuaxia in wet seasons. In dry seasons, the coefficients in spring tidal were higher than those in neaps tidal from Xiaoshan to Langshashan and the law was contrary from Xuliujing to Shihuaxia. The tidal limit was the boundary that the downstream coefficients of it were increasing. The coefficients in North Channel were higher than those in South Channel and the coefficients in North Passage were higher than those in South Passage. The main reason of this phenomenon was the temporal and spatial variation of driving forces of runoff and tide. The water depth of 15 m was thinking as the demarcation of point bars and deep troughs. The momentum coefficients increased with the increase of the water depth in the point bars and the coefficients didnt change much in the deep troughs. The empirical curve was also established.