Abstract: This study aims to clarify the effects of reduced mechanical side-deep fertilization (the technology primarily involves the simultaneous application of fertilizers while transplanting, distributing them evenly and in a precise quantity at a location 3 to 5 cm to the side of the rice root system and 4 to 6 cm deep) on rice yield, nutrient accumulation, economic benefits, and fertilizer use efficiency, providing a theoretical basis for mechanized rice production and the reduction and enhancement of chemical fertilizers. Multi-site field experiments were conducted in typical rice-growing areas in Hubei Province, China, in 2021. Seven treatments were established: 1) CK (Control, no fertilization); 2) CF (Conventional fertilization); 3) 100%DF (Deep placement fertilization at the same rate as CF); 4) 90%DF (Deep placement fertilization at 90% of CF rate); 5) 80%DF (Deep placement fertilization at 80% of CF rate); 6) 70%DF (Deep placement fertilization at 70% of CF rate); 7) 60%DF (Deep placement fertilization at 60% of CF rate). The rice yield, yield components, and nutrient content of different treatments were tested and analyzed to calculate nutrient accumulation, fertilizer use efficiency, and economic benefits. The results showed that: 1) Compared with the CF treatment, the 100%DF treatment significantly increased rice yield, with an average increase of 7.2%. Notably, plots with higher soil organic matter exhibited a more pronounced response, and the yield improvement was positively correlated with soil organic matter content. In Tianmen city, the rice shoot N and P accumulation under 100%DF increased significantly by 11.5% and 15.6%, respectively, compared to CF. In Zhijiang City, P accumulation increased significantly by 11.1%. In addition, the partial factor productivity of fertilizer at the Tianmen, Zhijiang, and Shayang sites was significantly improved by 7.5%. The output value and net income of rice were also significantly increased by 7.7% and 11.8%, respectively. 2) Mechanical side-deep fertilization demonstrated clear potential for fertilizer reduction. The optimal fertilizer reduction range varied across sites depending on soil fertility, with stable yields maintained even when the fertilizer rate was reduced to 60%DF-80%DF. Comprehensive analysis showed that under 90%DF and 80%DF treatments, grain yield and economic returns were not significantly different from CF, while partial factor productivity was significantly improved by 12.4% and 21.6%, respectively. In summary, the 100%DF treatment exhibited significant yield-enhancing potential under the tested conditions, whereas the 80%DF treatment effectively reduced fertilizer input while maintaining stable yield and improving fertilizer use efficiency. These findings suggest that mechanical side-deep fertilization is a promising strategy for achieving high yield and efficient fertilizer use in rice production.