The invention relates to the technical field of an oil chemical industry, and particularly discloses an environment-friendly dispersing agent for treating oily sludge and a preparation method thereof. The environment-friendly dispersing agent comprises the following raw materials in percentages by weight: 5-20 wt% of a cationic surfactant, 5-33 wt% of silicate, 1.5-10 wt% of inorganic salt and 37-88.5 wt% of water, and the sum of the contents of the components is 100 wt%. The method comprises the step of evenly mixing the cationic surfactant, silicate, inorganic salt and water to obtain the oily sludge dispersing agent. The environment-friendly dispersing agent disclosed by the invention has the advantages of good dispersion effect, high oil recovery rate, low production cost, environmental protection, simple and convenient preparation method and wide application range.