[Objective] The effects of different planting and overturning of winter green fertilizer on soil nitrogen supply capacity were studied in order to provide theoretical basis for improving planting technology of winter green fertilizer, increasing crop yield and maintaining soil productivity in North China. [Methods] A field experiment with a winter green manure-maize rotation was conducted at Wuqing District, Tianjin City from 2012 to 2019. The study also included indoor incubation experiments. The treatments included winter fallow, february orchid, vetch, rye, ryegrass, mixed vetch and february orchid, and mixed vetch and rye. Soil organic nitrogen content and its composition, soil organic nitrogen mineralization potential (N₀), and mineralization amount were measured. The effects of winter green manure planting and incorporation on soil organic nitrogen composition and mineralization were analyzed with winter fallow used as the control. [Results] Compared with winter fallow, winter green manure significantly increased total organic nitrogen and acid hydrolysable organic nitrogen by 3.05%—12.36%. However, winter green manure significantly decreased the content of non-acid-decomposed organic nitrogen by 18.87—55.87 mg/kg. N₀ was 189.15—245.90 mg/kg in the treatments with winter green manure (14.16%—48.41% greater than the control), and, half-life was increased by 22.57%—73.11%. After 24 weeks of indoor culture, soil organic nitrogen for all treatments was mainly composed of acid hydrolysable organic nitrogen. The mineralization amount of acid hydrolyzed total nitrogen was 3.41—20.54 mg/kg greater in the winter green manure treatments than that in the control, and the mineralization rate was 7.96%—47.31% higher than that in the control, with significant differences. [Conclusion] Winter green manure planting and incorporation significantly increased soil organic nitrogen storage and mineralizable nitrogen content, and prolonged the mineralization cycle, thereby promoting the renewal of the soil nitrogen pool, and improving soil nitrogen availability.