The invention discloses a preparation method of a low-temperature oxygen bleaching activator. The method comprises the two steps of synthesizing an intermidate and generating the low-temperature oxygen bleaching activator: 1) adding a diamine compound, an organic amine neutralizer and a solvent A into a four-opening flask; heating until realizing solvent A reflux; 2) dissolving 4-dimethylamino benzoyl chloride with the solvent A; adding into the four-opening flask; preserving heat and refluxing for 5 to 6 hours; 3) cooling and separating out a precipitate; performing suction filtration, washing and drying on the precipitate, thereby obtaining the intermidate; 4) adding the intermidate and a solvent B into the four-opening flask; slowly dripping dimethyl sulfate for 1 to 2 hours; continuously stirring for 1 to 2 hours after dripping; 5) removing the solvent in a steaming manner, thereby obtaining the low-temperature oxygen bleaching activator. When the low-temperature oxygen bleaching activator is used for structuring a hydrogen peroxide and activator scouring and bleaching system, the whiteness of a fabric can reach the level of conventional bleaching; the handfeel of the fabric is superior to that obtained by the conventional bleaching. Thus, the damage to the fabric is reduced; the energy consumption is decreased; the production efficiency is improved.