Abstract: Objective: This study aimed to develop a green and efficient formula for a composite phosphorus-free water retention agent to enhance the water-holding capacity of frozen Sebastes schlegelii fillets. Methods: The optimal ratio was derived from the optimization method of orthogonal experiments based on one-way experiments, using the soaking weight gain rate, thawing loss rate, and cooking loss rate as evaluation indices of water retention. This approach allowed for the determination of the optimal compound phosphorus-free water retaining agent formula. The water retention effect, texture characteristics, microstructure, and sensory quality of the fish fillets treated with the optimal compound non-phosphorus water retaining agent formula were analyzed. Results: The results indicated that the optimal combination of the formula consisted of 2.5% sodium bicarbonate, 2.0% sodium citrate, and 1.5% alginate. Following treatment with this compound phosphorus-free water retention agent, the soaking weight gain rate of Sebastes schlegelii fillets increased from 5.46% to 19.2%, while the thawing loss rate and cooking loss rate decreased from 9.23% and 30.6% to 1.28% and 14.0%, respectively. These results were comparable to those of fillets treated with the compound phosphate water retention agent in terms of texture and structure. Microstructural analysis revealed that this formula helped maintain the integrity of the muscle fibers in the fillets, reducing the destruction of muscle fibers after thawing, while also effectively improving sensory quality and mitigating the negative sensory impacts associated with phosphate treatment. The composite phosphorus-free water retention agent formula developed in this study demonstrated its feasibility as a replacement for traditional phosphates. This achievement provides a theoretical basis for the industrial application expansion of phosphorus-free water retention technology in the processing of Sebastes schlegelii products.