Abstract: Maize and oats are the main forage crops in northern China, valued for their high feed utility and economic significance. To optimize fertilization strategies for forage production in the Hulunbuir region, this study investigated the effects of gradient organic fertilizer nitrogen substitution treatments (0%, 25%, 50%, and 75% substitution rates) on local mainstay crops—maize and oats. A comprehensive assessment was conducted on crop yield, nutritional quality, and environmental impact under different fertilization regimes.The results showed that organic fertilizer substitution significantly influenced maize yield. The 50% organic fertilizer substitution treatment increased maize yield by 28.9% compared to the full chemical fertilizer treatment, and notably reduced the contents of cellulose and acid detergent fiber in maize stems. In contrast, oat yield did not differ significantly among treatments. Nutritional quality analysis indicated that the 75% organic fertilizer substitution treatment enhanced oat crude protein content. Life cycle assessment revealed that the 50% substitution treatment for maize and the 75% substitution treatment for oats resulted in lower environmental costs.A comprehensive evaluation based on the membership function method identified 50% organic fertilizer substitution as the optimal fertilization strategy for both maize (membership value: 0.539) and oats (membership value: 0.626). These findings provide theoretical support and data-driven guidance for the development of eco-friendly forage production systems.