Abstract: Red kidney bean is often confined to the low release of nutrients and functional components in the whole powder. In this study, a combination of microwave ripening and cellulase hydrolysis was employed to process the raw materials of the red kidney bean. The processing parameters were optimized to enhance the nutritional and functional properties of the final products. Five key factors: microwave power, microwave time, amount of enzyme added, enzyme digestion time, and enzyme digestion temperature were selected as the independent variables. The dependent variables included the average temperature, water content, dietary fiber content, total phenol content, and antioxidant properties of the red kidney bean whole powder. A central combinatorial experiment was introduced to systematically analyze the influence of these factors on the target quantities. Additionally, the hierarchical analysis-objective hybrid weighting (AHP-CRITIC) was combined with the response surface method (RSM) to evaluate the interaction of the processing parameters. The results revealed that there was a synergistic effect in the combination of the microwave ripening and cellulase hydrolysis. The nutrient utilization rate was significantly improved for the functional properties of red kidney bean whole powder. Microwave treatment was found to enhance the efficiency of the cellulase hydrolysis, thus leading to the release of the soluble dietary fiber, total phenols, and antioxidant compounds. The nutritional profile of the functional powder was enhanced for the more valuable ingredient of the food applications. The optimal processing parameters were determined for the microwave ripening-cellulase hydrolysis of red kidney bean whole powder: the microwave power of 440 W, microwave time of 10 minutes, enzyme addition of 2.0%, enzyme digestion temperature of 55 °C, and enzyme digestion time of 2 h. The superior nutritional and functional properties were achieved after optimization. Specifically, the soluble dietary fiber content of the optimal red kidney bean whole powder reached 8.26 g/100 g, indicating an 87.3% increase, compared with the conventionally processed powder. The total phenol content was measured at 485.58 mg/100 g, with a 31.56% improvement over the control. The comprehensive score of the optimal product was 140.53 points, indicating its overall superiority in the nutritional quality and functional performance. The microwave ripening and cellulase hydrolysis can be expected to enhance the nutritional and functional properties of the red kidney bean whole powder. There was a significant increase in the soluble dietary fiber, total phenols, and antioxidant activity. The combined treatment improved the nutrient availability to enhance the health-promoting properties of the powder. The optimal red kidney bean whole powder can serve as a high-quality ingredient for functional foods, dietary supplements, and health-oriented products. Furthermore, there were valuable insights into the underlying mechanisms of the synergistic effects of microwave ripening and cellulase hydrolysis. Microwave treatment was found to disrupt the cell wall structure of the red kidney beans, where the dietary fiber and phenolic compounds were more accessible to enzymatic hydrolysis. In turn, the soluble dietary fiber and bioactive compounds were released in the nutritional and functional properties. The processing parameters were optimized to maximize the benefits of these treatments. In conclusion, the optimal process parameters were achieved with the significantly enhanced soluble dietary fiber content, total phenol content: the microwave power of 440 W, microwave time of 10 minutes, enzyme addition of 2.0%, enzyme digestion temperature of 55 °C, and enzyme digestion time of 2 h. The nutritional value of red kidney bean whole powder can be expanded to its potential applications in the food industry. The findings can provide a theoretical foundation and practical reference for the high-quality whole powder products of the red kidney bean, thus offering new opportunities for the utilization of nutritious legumes in functional foods and health-promoting products.