The growth performance of individual plants in a population was well recognized to be affected by the plant–plant interactions, which we called neighborhood interference. Though relevant mechanisms are still unclear, the variations in gas exchange parameters in relation to the neighborhood interference between individual plants are crucial for evaluating the effects of plant plant interactions. CO2 assimilations in leaves of teak under natural conditions during dry season (November to next April) and wet season (May to October) and its responses to variations in light flux density and CO2 concentration in different neighborhood interference were simultaneously measured with Li-6400 portable photosynthesis system in a 21-years old tropical plantation forest at Jianfengling, Hainan Island. This article deals with the rule of the changes of neighborhood interference on trees characteristics of gas exchange and its dynamic responses to light environments by individual plants. Empirical models of photosynthetic light response and photosynthetic CO2 response were developed to predict the daytime carbon gain by fitting measured data into a non-rectangular hyperbola nonlinear model with the following parameters: the light-saturated photosynthetic rate (Asat), the light-saturated constant (K, equal to the PPFD, which is required to produce one-half of the light-saturated photosynthetic rate), apparent quantum yield (αA, the initial slope of the curve) and dark respiration rate (Rd). Values of the parameters of the maximum rate of carboxylation by Rubisco (Vcmax), carboxylation efficiency (CE), the PAR saturated rate of electron transport (Jmax) were estimated use these models. Diurnal courses of photosynthesis of individuals were not affected by neighborhood interference, but net photosynthetic rates showed a negative relationship with the intensity of neighborhood interference. The ratio of daily average Pn in weak, moderate, strong and heavy neighborhood interference was 2.5∶2.3∶1.7∶1.0, and daily maximum of Pn in weak interference was 2.8 times of that in heavy interference. Leaf transpiration and stomatal conductance were decreased with the increasing of interference intensity. Characteristics of photosynthetic light response and CO2 response was changed by the neighborhood interference, and values of leaf gas exchange parameters including Asat , Qsat, αA, CE, Vcmax and Jmax in weak interference were enhanced by 2.7, 1.3, 1.4, 2.7, 1.9 and 2.8 times respectively than those in heavy interference. But the changes in those parameters were partly depended on light environment and CO2 concentrations, the influence resulted from the changes in light environment on weak interference individuals was significantly stronger than on heavy interference. While beyond the growth CO2 concentrations, the influence resulted from the changes in CO2 concentration on heavy interference individuals was obviously stronger than on weak interference. In conclusion, neighborhood interference can be described as a major means of intra-specific competition of population in a plantation forest with uniform forest structure and consistent management. Carbon assimilation will be affected by the neighborhood interference, and result in divergence in growth performance. Indices of neighborhood interference can be used to evaluate the intra-specific competition, and make the maximum usage on resources after stand structure well adjusted based on that.