The invention discloses a brownification fluid for processing a printed circuit board on the basis of a functionalized ionic liquid. The brownification fluid is characterized by comprising raw materials by mass concentration as follows: sulfuric acid with the concentration of 80-120 g/L, hydrogen peroxide with the concentration of 5-25 g/L, an ionic liquid corrosion inhibitor with the concentration of 5-25 g/L and an ionic liquid binding force accelerant with the concentration of 0.5-5.0 g/L, wherein the ionic liquid corrosion inhibitor is an ionic liquid with alkyl or amino substituted benzimidazole as cations and halogen as anions. The copper loading capacity of the brownification fluid can reach 60 g/L, a uniform and coarse surface can be obtained after the copper surface is subjected to brownification processing, and the binding force between the copper surface and a prepreg is stable. The defects that haloid has to be added in a conventional brownification fluid and the like can be avoided by regulating the anions of the ionic liquid, and the brownificaiton fluid has remarkable environmental friendliness and excellence due to environment friendliness and non-volatility of the ionic liquid.