Based on the physical model test of closed and rectangular flume with pressure，we carry out the scour test of undisturbed soil of silt in the channel of the Yangtze River estuary to analyze the starting and scour characteristics of undisturbed soil and the influence of the depth of soil sample on the scour effect of soil sample.The results show that the density of soil sample almost keeps constant before and after scouring，and because of a smaller proportion of sand in the eroded soil，the soil density after scouring performs slightly smaller. Besides，the critical incipient shear stress increases with the increasing critical incipient velocity，the two can satisfy the exponential relation with each other，and the fitting of function is excellent. When the depth of soil increases，both scour rate and scour coefficient decrease which illustrate the uneven distribution of bottom silt along the depth of the Yangtze River estuary channel，the deeper silt has a larger scouring resistance while surface silt has the more unstable the particle composition and is more easily to be eroded.