The present invention provides a composition of hydraulic fluid that mainly contains alkyl benzenes. In addition to alkyl benzenes, the composition also contains an antioxidant, an antifoaming agent, a pour point dispersant, a corrosion inhibitor and a detergent-dispersant additive, an extreme pressure additive, a lubrication additives, comprising of the following steps (I) removing of insoluble matter from the base stock, (II) tailoring the base stock by vacuum distillation and blending, (IV) removing the oxidized matters by adsorption, (V) addition of performance additives and homogenizing the mixture. The product of this invention has utility as an general purpose hydraulic fluid.