The invention relates to the technical field of industrial cleaning agents, is an improvement of the prior art, and particularly relates to a nano water-based cleaning agent and a preparing method thereof. The cleaning agent comprises, by weight, 2.0% to 18.0% of saponifiers, 5.0% to 30.0% of surfactants, 0.05% to 0.5% of inhibiters, 0.05% to 0.5% of nano defoamers, 0.2% to 1.0% of water-soluble nano silica and the balance deionized water, wherein the total weight percentage is 100%. The nano water-based cleaning agent and the preparing method thereof are characterized in that bubbles during a cleaning process are few, water rinsing is not needed after cleaning, the cleaning procedure is reduced, and the energy is saved and the cost is reduced; and volatile organic solvents are not contained, cleaned objects are not corroded, the application range is wide, and heat dissolution is not needed during the preparation so that energy is saved. The nano water-based cleaning agent and the preparing method thereof are practical and large in market potential.