The present invention disclose a method for preventing discoloration of walnut during cooking by adding caustic soda, a cooking process of walnut porridge of which discoloration is inhibited, and walnut porridge prepared by the same. The addition of the caustic soda neutralizes tannic acid contained in the inner shell of the walnut causing discoloration of walnuts during cooking. The inventive walnut porridge retains the walnut's intrinsic color, having experienced the least discoloration into dark greyish color during cooking, and exhibits enhanced sensory attributes without losing its natural taste.