The purpose of this study is to explore the potential changes in the relationship between dynamic light and photosynthesis in high CO₂ environment, so as to provide scientific support for coping with global changes. We characterized dynamic light environment at two heights within rice canopy and dynamic photosynthetic response of leaves at each height (about 45 cm or 90 cm high from the soil of paddy field) in an open canopy and within an open top chamber (OTC) with a high CO₂ of 600 μmol/mol air. The result showed that the averaged photosynthetic photon flux density incident at 90 cm height above the paddy field was 3–4 times higher than that at 45 cm height, but the coefficient of temporal variation in light received at 90 cm height was 55%–60% smaller than that of the lower layer. Flag leaves at 90 cm height showed higher saturated photosynthetic rate and more postillumination CO₂ fixation, while leaves at 45 cm height showed higher photosynthetic rate under low light. In the high CO₂ OTC, light attenuation percentage in canopy tended to increase, compared with leaves outside the OTC; the difference between assimilation rates at the two heights also increased within the OTC. These results suggested that not only the steady-state photosynthetic rate, but also the dynamic photosynthesis in rice leaves may have altered in different ways at different canopy heights, which is to be further influenced by CO₂ environment.