To study the lethal effect of different sizes and burial depth of the dredged materials on creatures residing in the ocean, our research buries Ruditapes philippinarum and Perinereis aibuhitensis using different size and depth of the dredged materials in the Yangtze Estuary to analyse the survival rate. The results showed that they survive by vertically migrating out of the dredged materials, and there is significant positive correlation between burial depth and mortality of Ruditapes philippinarum within a certain scope. When the size of burying material is 63-125 μm, the 96h -LC₅₀ of Ruditapes philippinarum was 6.8 cm(95% confidence interval was 2.8-10.7 cm); When the size of burying material is under 63 μm, the 96h -LC₅₀ of Ruditapes philippinarum was 11.1 cm(95% confidence interval was 4.2-18.0 cm); howerer, there is no significant correlation between burial depth and mortality of Ruditapes philippinarum. The study results prove that the size and burial depth of the dredged materials have different lethal effects on different benthos.