Rice straw returning is an effective strategy for soil amelioration, fertility enhancement, and agro-ecosystem conservation. Straw returning combined with chemical fertilizer application synergistically improves soil productivity and crop yields. Using Jigeng 81 as experimental material, we systematically compared the effects of five fertilizer-density treatments on paddy soil quality and rice yield under long-term straw returning through a positioning experiment. The results showed that prolonged straw returning significantly enhanced soil physicochemical properties. Compared with initial values, contents of total nitrogen, total phosphorus, total potassium, available nitrogen, available phosphorus, available potassium, and organic matter increased substantially, while soil pH demonstrated a decreasing trend. These changes collectively indicated remarkable improvement in soil comprehensive quality. Among the five treatments, T3 treatment(20% increased density+conventional fertilization) and T5 treatment (20% increased density+20% reduced nitrogen) exhibited pronounced yield-increasing effects. Notably, T5 treatment achieved 17.88% and 16.74% higher yields than T1 treatment (normal density + conventional fertilization) across two consecutive years. T5 treatment demonstrated superior agronomic efficiency and partial productivity of nitrogen fertilizer compared to other treatments. This study demonstrated that under long-term straw returning, adopting a cultivation model combining 20% nitrogen reduction with 20% density increase (T5) could effectively balance yield, economic, and ecological benefits, thereby achieving increased yield, enhanced efficiency, and sustainable development in rice production.