A microscopic test study was carried out by taking the mud soil of Shenzhen Dachanwan as the sample. The study reveals that the dredged mud soil is obviously flocculent structure with a high void ratio and multiple holes, as well as an obvious water film of strong bound water at the particle boundary; Large aperture holes of mud after foundation dispose decrease obviously, and the small holes are also jammed, forming a more compact structure; The mud holes are of a great amount and rather big, resulting in a high probability of dewatering passageway connecting by holes. It is indicated from the permeation test that the osmotic coefficients are in the magnitude of 10-7~10-8 and with a low osmotic coefficient. So, if the continuous pores are thought to be the seepage passageway, there is a natural contradiction between the high porosity ratio and low osmotic coefficient; Holes in mud are in the majority of 5 滋m and below, especially 2 滋m and below. Water in holes is in the majority of weak bound water and capillary water; Osmotic coefficients of mud soil under electric field are changing along with voltage; Osmotic coefficients after foundation dispose are less than that before foundation dispose. Furthermore, the osmotic coefficients of mud under the control of effective aperture and bound water content are checked.