This paper aimed at the high-value utilization of walnut cake, a by-product of oil processing industry. The walnut protein (WP) was extracted by alkali extraction-acid precipitation method from cold-pressed walnut cake, then trypsin hydrolysis process was optimized by single factor experiment and orthogonal design, with degree of hydrolysis (DH) as the indicator. Subsequently, the decolorization process of WP hydrolysate was optimized with protein recovery rate and decolorization rate as the indicators. The results showed that the extracted walnut protein was of high purity and could be used for further enzymatic hydrolysis and decolorization tests. After optimization, the DH of WP could be increased to 21.08% under the following conditions: the substrate concentration of 3%, the hydrolysis temperature of 55 ℃, the enzyme addition of 6 250 U/g protein, and the enzymatic hydrolysis time of 5 h. The optimal process of decolorization of walnut protease hydrolysate was obtained at an activated carbon addition of 1.2% (W/V), a pH of 4.5, a adsorption temperature of 45 ℃, and a decolorization time of 90 min. Under these conditions, the decolorization rate of walnut protease hydrolysate was 78.05%, protein recovery rate was 82.16%, and the combined weighted mean score was 80.11. The optimization process of trypsin hydrolysis and decolorization could provide some references for the development and utilization of walnut cake.