AbstractThe photosynthetic rate is considered to be affected by individual biomass and limited by nutrients. Metabolic scaling models are often utilized to predict photosynthetic rates based on plant size and other factors, such as temperature and plant nutrient composition. However, the intrinsic regulatory mechanisms of the combined factors that affect the photosynthetic rates of living organisms are subject to debate. Here, we present a model developed from the metabolic scaling model, the Michaelis‐Menten equation and elemental stoichiometric models to precisely predict the relationship between plant photosynthetic rate and biomass. The developed model was verified against data for small woody and nonwoody plants, and in comparison with the typical metabolic scaling model, this model was shown to be more capable of explaining the photosynthesis‐biomass relationship. Moreover, the results showed that the combined factors affected photosynthesis via the regulatory effect of nutrients on photosynthesis‐biomass allometry. We highlight that nutrients have direct effects on the allocation of plant biomass and photosynthetic investment under stable and balanced growth states.