Abstract: Sludge electrolytic dehydration has its unique advantages, but at the same time accompanied by high power consumption, low space-time yield and other problems. In order to reduce energy consumption, taking the change of mud cake thickness in the process of sludge electrolytic dehydration as the starting point, the rule of thickness change and the relationship between thickness change and water content were explored through the small test device. The change of water content was more intuitive and controllable by observing thickness change in sludge electrolysis process under the action of vertical electric field. The mechanism of thickness change was briefly analyzed from the density and moisture content. The experiment proved that the thickness of mud cake changed regularly during the process of electrolysis. When the amount of mud input was less, the thickness of mud cake decreased with the decrease of water content, while when the amount of mud input was larger, the thickness of mud cake increased firstly and then decreased with the decrease of water content.