The invention discloses a method for recycling iron waste for the fenton technology. The method comprises the following steps that hydrogen peroxide, the iron waste and an activating agent are added to waste water to be treated, stirring is conducted so that the iron waste can be dispersed in a reaction system, a reaction is conducted, and then solid and liquid separation is conducted, wherein the activating agent is any one or a mixture of sodium sulfite, potassium sulfite, magnesium sulfite, calcium sulfite, sodium thiosulfate, potassium thiosulfate, calcium thiosulfate, magnesium thiosulfate, sodium borohydride, potassium borohydride, hydroxylamine hydrochloride and ascorbic acid. By means of the method, various kinds of iron waste are recycled, meanwhile, zero iron mud emission is achieved, and thus pollution to the environment is effectively reduced. The invention further provides a water treating device capable of achieving the method. By means of the method and the water treating device, the reaction speed of the iron waste in the fenton system is greatly increased, the effective pH range of the fenton system is expanded, meanwhile zero iron mud emission is achieved, and thus pollution to the environment can be easily reduced.