During a tidal cycle,the back-siltation is changing with the tidal power.So it is necessary to study the distribution of back-siltation in the deep channel.The result is helpful for the arrangement of channel maintenance to reduce unnecessary dredging.Based on the hydrological data observed near the bottom of the deep water channel,a model is used in this paper and the distribution characteristics and mechanism of back-siltation is obtained.Although the sediment concentration near the bottom is high and the bed is eroded by the strong power during the spring tides obviously,the formation of back-siltation is smaller.And the back-siltation mainly occurs during neap tides.This conclusion has been verified by the data observed during the dry season.