Belonging to the technical field of hydraulic oil, the invention discloses a high-identification degree hydraulic oil and a preparation method thereof. The hydraulic oil is composed of the following components by weight: 100 parts of pure hydraulic oil, 0.1 part of an antioxidant, 0.1 part of an extreme pressure anti-wear agent and reactive blue 19 accounting for 5ppm of the total mass of the hydraulic oil. The preparation method of the high-identification degree hydraulic oil includes the steps of: S1, by weight, putting 30 parts of N, N-dimethyl-formamide and 60 parts of furfural into a reaction kettle, and stirring the substances uniformly at room temperature to obtain an extraction agent; S2, introducing base oil and the extraction agent jointly into a centrifugal extracter according to a proportion of 1:1, performing extraction at 40DEG C for 1h, at the end of the extraction, separating the base oil from the extraction agent at 40DEG C to obtain pure hydraulic oil. The preparationmethod provided by the invention is simple and practicable, is low in preparation cost, and is suitable for large scale preparation of hydraulic oil, also the prepared hydraulic oil is bright and full in color and easy to observe, and is free of sediment or impurity, has strong oxidation resistance and lasting coloring effect.