Plant photosynthesis and respiration are key processes of ecosystem carbon cycle. The variation characteristics and influencing factors of CO₂ δ¹³C can provide theoretical basis for the analysis of plant carbon allocation patterns, key metabolic processes, and the decomposition of photosynthetic and respiratory components in ecosystems. However, there is still a lack of clear understanding of photosynthetic and respiratory CO₂ and its variation characteristics and influencing factors of δ¹³C at different time scales. From the aspects of plant carbon process and its isotope effect, observation techniques and methods, variation characteristics and influencing factors, application practice and research progress, the obviously diurnal and seasonal variation of CO₂ assimilation rate and its δ¹³C in plant carbon photosynthesis and respiration process were summarized. The effects of biotic factors such as stomatal, mesophyll and carboxylation restriction, as well as abiotic factors such as temperature, humidity and light on carbon processes and their isotopic effects were discussed. The existing problems were summarized and the future research directions were prospected in order to provide theoretical basis and effective support for the future research in this field.