Embodiments of the invention disclose a method for preparing an aqueous nano-pigment dispersion. The method comprises mixing 2.5 wt %˜40 wt % styrene with polymerization inhibitors removed by evaporation, 2.5 wt %˜20 wt % acrylate monomer, 0.25 wt %˜5 wt % crosslinking monomer, 0.05 wt %˜0.5 wt % emulsification adjuvant, and 0.05 wt %˜0.5 wt % oil soluble initiator, adding 0.25 wt %˜2.5 wt % organic pigments to be dispersed to form an oil phase solution after dissolution; dissolving 0.05 wt %˜2 wt % emulsifier and 0.05 wt %˜2 wt % buffer in 40 wt % wt˜90 wt % deionized water to form an aqueous solution; mixing the oil phase solution and the aqueous phase solution, and then homogenizing them into fine emulsion; transferring the fine emulsion into a reactor; heating to increase the temperature to initiate the polymerization; after reacting, adding an alkaline soluble monomer; after continuing the reaction, cooling the temperature to the room temperature; adjusting pH to weak alkaline; and filtering to obtain the aqueous nano-pigment dispersion.