Developing an environmentally friendly material with dual functionality of corrosion monitoring and inhibition is crucial for reducing economic losses. Herein, dual-function phytic acid carbon dots (PA-CDs) were prepared with a hydrothermal treatment method for corrosion monitoring and inhibition. The as-prepared PA-CDs exhibited a distinct color change from brown-yellow to wine-red immediately in the presence of OH⁻, and H⁺ can restore the color of the PA-CDs-OH⁻ system from wine-red to brown-yellow. Inspired by the above phenomenon, a visible RGB-based colorimetric sensor was fabricated by combining PA-CDs coatings with the self-made RGB-sensing device to detect OH⁻/H⁺ during metal corrosion. In addition, PA-CDs had excellent corrosion inhibitory properties for Q235 steel hanging sheets in hydrochloric acid solutions, and the corrosion inhibition efficiency reached 96.40%. The excellent corrosion monitoring and inhibition properties demonstrate the potential application of the PA-CDs in engineering practice.