A Plant Functional Group (PFG) is composed of a set of plants co-existing within a community and can serve as a basic unit of vegetation dynamic change within an environment and can act to simplify related research. The physiological characteristics of different species provide the basis for PFG classification and also affect the overall function of PFGs. The forest ecosystem has structural integrity in the National Natural Reserve of FuNiu Mountain. Through species' interspecific associations and their dynamic changes along the elevation gradient, we classified the dominant species into four major PFGs. We then analyzed the photosynthetic characteristics of each plant of the four PFGs. Using the photosynthesis system, we measured the photosynthetic characteristics of different plants of PFGs and analyzed and compared the results which show: that the maximum Coefficient of Variation of different species' LCP(light compensation point) and Rd(respiration rate) was 70.47% and 74.29% respectively within the same PFG; these are complementary to each other among functional traits, which is the main reason for the long-term coexistence of the PFG. Trees' Pn(maximum net photosynthetic rate) was between 7 and 8 CO₂ m^-2 s^-1 which suggests that they have the ability to capture high-intensity light LSP(Light saturated point) within the same PFG was mainly between 1200-1500μmol m^-2 s^-1, which differs very little. Herbaceous understory shrubs are more sensitive to low-intensity light than the trees. There are functional characteristic differences among the same PFG and between different PFGs, which affects the structure, function, processes, and ecosystem services of the forest ecosystem.