The invention provides a sludge deep dehydration method comprising the following steps: adding 1-10%, based on the dry weight of sludge slurry, of a free radical production into the sludge slurry, and stirring to mix; adding a transition metal salt activator, a magnesium salt activator and / or an aluminum salt activator to the sludge slurry containing the free radical production, carrying out an activation reaction to form active free radicals, and treating by the active free radicals to obtain a conditioned sludge slurry; and dehydrating the conditioned sludge slurry. Through the sludge deep dehydration method, the active free radicals are produced by reacting the transition metal salt, the magnesium salt and / or the aluminum salt and the like with the free radical production, on one hand, can effectively destroy sludge extracellular polymeric substances, alter surface properties of sludge particles, improve the filtration performance of the sludge, and reduce the sludge bound water content; on the other hand, the active free radicals can active ions produced after the completion of the reaction, can be combined with sludge particles, can improve the strength of sludge flocs, are favorable to the sludge dehydration process, so as to realize the sludge deep dehydration.