Elevated atmospheric CO2 concentrations (e[CO2]) have a profound impact on crop production. However, within the e[CO2] trend, the influence of different nitrogen (N) application rates on the photosynthetic efficiency of rice leaves, as well as the resulting changes in grain yield, remains poorly understood. Open-top chambers (OTCs) were utilized as the research platform; there were three [CO2] treatments, i.e., ambient [CO2] treatment as the control group (CG, 400 ± 10 mmol mol–1); C1 (560 ± 10 mmol mol–1); and C2 (600 ± 10 mmol mol–1); and three levels of nitrogen fertilizer, N1, N2, and N3 (100, 200, and 300 kg ha− 1). Chlorophyll fluorescence (ChlF) technology was used to study the variations in photosynthetic parameters during the crucial growth stage of rice and to analyze yield composition disparities. The findings demonstrated that the level of e[CO2] and nitrogen fertilizer dose significantly influenced the chlorophyll content and photosynthetic efficiency of rice leaves throughout the growth period, ultimately impacting yield composition. Moreover, a notable positive interaction effect between these two factors was observed. Compared with CGN1, N2 and N3 had greater leaf maximum photochemical quantum efficiency (Fv/Fm) and energy transformation potential (Fv/Fo). Relatively speaking, nitrogen fertilizer had a more significant effect than e[CO2]. Overall, e[CO2] can undeniably enhance rice photosynthesis and ultimately lead to increased yield, but it is imperative to also focus on augmenting the application of nitrogen fertilizer.