The open-top chamber (OTC) is an important device used to study the impact of climate change on ecosystems. These chambers have been widely used in climate change simulation and pollution ecology research. Compared to the conventional closed artificial climate chamber or the newly developed free-air concentration enrichment (FACE) method, the OTC creates a microclimate that is more similar to the atmospheric environment. Moreover, its test gas concentration control is more precise, and its construction and operating costs are lower. Our research results indicated that microclimatic elements inside and outside the OTC are different. Although much research has been carried out on microclimatic elements inside and outside the OTC, and improvements have been made based on these research results, there are only a few reports on the growth and photosynthetic response of plants to these microclimatic differences.This study aimed to evaluate the photosynthetic response of winter wheat (Triticum aestivum L.) grown inside (T1) and outside (T2) an OTC, using the plants of a modern cultivar, 'YangMai16.’ Gas exchange, photosynthetic pigment content, and chlorophyll fluorescence parameters were evaluated. The test field was located at the Agricultural Meteorological Experiment Station of Nanjing University of Information Science and Technology, China (32°03'N, 118°51'E). The seeds were sown on November 5, 2009, by drilling, with a seeding rate of 220.5 kg/hm², and plants were harvested on May 31, 2010. The daily mean temperature and relative humidity inside the OTC used in our experiments were 8.9% and 3.3% higher, respectively, than those of the atmospheric environment; however, total radiation was 20.4% lower. The differences in microclimatic elements inside and outside the OTC used in this study were similar to those recorded by other groups.Our results indicated that the net photosynthetic rate (P_n), stomatal conductance (G_s), intercellular CO₂ concentration (C_i), max photo-synthetic rate (P_m), and half-saturation light intensity (I_k ) of T1 were significantly higher than those of T2 (P<0.05). Before the filling stage, the apparent quantum yield (AQY) of T1 was significantly higher than that of T2, whereas transpiration rate (T_r) and dark respiratory rate (R_d) were significantly lower (P<0.05). After the filling stage, the results reversed. The chlorophyll and carotenoid contents of T1 were significantly higher than those of T2 during most of the growth stages P<0.05). The basic fluorescence yield (F_o) and dark-adapted maximum fluorescence yield (F_m) values of T1 were higher than those of T2, but there was no difference in the maximum photochemical capacity of PSⅡ (photosystem II) (F_v/F_m) between T1 and T2 during most of the growth stages. In the booting and flowering stages, the photochemical quenching coefficient (qP) of T1 was significantly lower than that of T2 (P<0.05). There was no difference in the quantum yield of photochemical energy conversion in PSⅡ [Y_(II)]of T1 and T2 during most of the growth stages. The non-photochemical quenching coefficient (NPQ) and quantum yield of regulated non-photochemical energy loss in PSⅡ [Y_(NPQ)] of T1 were significantly higher than those of T2 after the filling stage (P<0.05), whereas the quantum yield of non-regulated non-photochemical energy loss in PSⅡ [Y_(NO)] was lower. Our results indicate that the gas exchange capability, light response capability, and photosynthetic pigment content of winter wheat grown inside the OTC were higher than those of wheat grown outside. There were no differences in the maximum photochemical capacity and quantum yield of photochemical energy conversion in the PSⅡ of winter wheat grown inside and outside the OTC. In contrast, the fraction of energy dissipated as heat via the regulated photo-protective NPQ mechanism was higher, while the fraction that was passively dissipated in the form of heat and fluorescence was lower, for winter wheat grown inside the OTC. Photo-protection of the photosynthetic apparatus from excess energy in PSⅡ was also better in the winter wheat grown inside the OTC. Our results are expected to help improve OTCs, including the evaluation of data from controversial ecology projects and the application of research knowledge obtained from OTCs to field conditions.