Abstract: Exploring the ammonia emission reduction effect resulting from different application ratios of urea to controlled-release fertilizers may provide a theoretical basis for achieving ammonia emission reduction in farmlands, increase crop yields, and enhance the economic benefits of farmers. Field experiments were conducted in a typical maize-oilseed rape rotation system in Deyang City, Sichuan Province, China, from 2022 to 2024. Under the condition of equal nitrogen (N) application 180 kg(N)∙hm⁻², six treatments with different ratios of urea and controlled-release fertilizer were formed: a control without N addition, 100% urea, 70% urea + 30% controlled-release fertilizer, 50% urea + 50% controlled-release fertilizer, 30% urea + 70% controlled-release fertilizer, and 100% controlled-release fertilizer. Based on continuous monitoring of soil ammonia volatilization conducted using the closed-chamber intermittent ventilation method during the crop growth period, we compared the ammonia emission reduction effects of different combination ratios of urea and controlled-release fertilizer, as well as their impacts on yield, nitrogen use efficiency, and economic benefits. The cumulative ammonia volatilization in the maize season ranged 7.8–50.1 kg(N)∙hm^−2. Compared to the application of urea alone, the ammonia volatilization was significantly reduced by 31.0%, and the economic benefits were significantly increased by 19.7% when the proportion of controlled-release fertilizer added was 70%. When the proportion of controlled-release fertilizer was 100%, the cumulative ammonia volatilization was significantly reduced by 47.5%, the yield was increased by 13.4%, the nitrogen agronomic use efficiency significantly improved by 58.2%, and the economic benefits were significantly enhanced by 24.8%. The cumulative ammonia volatilization in the oilseed rape season ranged 4.9–59.0 kg(N)∙hm⁻². Compared to the application of urea alone, when the proportion of controlled-release fertilizer was 30%, the ammonia volatilization was significantly reduced by 25.1%, the yield was increased by 10.7%, the nitrogen agronomic use efficiency was significantly improved by 32.6%, and the economic benefits was significantly enhanced by 26.4%. When the addition proportion of controlled-release fertilizer was 70%, the cumulative ammonia volatilization was significantly reduced by 28.2%, the yield was increased by 9.9%, the nitrogen agronomic use efficiency was significantly improved by 51.0%, and the economic benefits was significantly enhanced by 19.6%. In summary, the single application of slow-controlled release fertilizer in maize season and the application of controlled-release fertilizer and urea in the ratio of 3∶7 in oilseed rape season are an economical and environmentally friendly fertilization mode, which can significantly reduce the ammonia volatilization, while simultaneously improving yield, nitrogen use efficiency, and economic benefits in the maize-oilseed rape rotation system.