In order to sample undisturbed riverbed sediments，a new type of bottom sampler is developed and applied to the study of back-siltation in the Yangtze estuary 12.5 m deep-water channel. The results show that the new bottom sampler has advantages in tightness，adaptability，success rate of sampling，quantity，and fidelity of sediment sample. The undisturbed sediment in the south channel （SC） and north passage （NP） includes sand，mud，mixed sand-mud，and layered sand-mud，and the types and variation characteristics of sediments reflect the sediment source and deposition process. Based on the grain size parameters of undisturbed sediment samples，the bedload transport trend in SC and the quantitative influence of bedload on back-siltation in the Yangtze estuary deep-water channel are studied.