Orchid species are densely distributed in some karst limestone hilltop areas in southwest China, in which they become the dominant species in the herbaceous layer with epiphytic orchids having greater advantages over terrestrial orchids in both species number and population size. However, the ecophysiological adaptation of these sympatric orchids belonging to different growth forms are not fully understood. In this study, photosynthetic characteristics, leaf mass per area, leaf chlorophyll content traits, leaf nitrogen content and nitrogen allocation strategies in leaves of 22 epiphytic orchids and six terrestrial orchids in a karst limestone hilltop area in Yachang Orchid National Nature Reserve in southwest China were compared. The results showed that compared with terrestrial orchids, epiphytic orchids had lower light-saturated photosynthetic rate, photosynthetic nitrogen use efficiency, chlorophyll content, chlorophyll a/b ratio, leaf nitrogen content and leaf nitrogen content in photosynthetic apparatus, indicating that epiphytic orchids allocated more resources (nitrogen) into the construction of leaves with stronger resistance at the expense of photosynthetic capacity. The combination of these functional traits fits well with surviving and thriving in the karst limestone environment, under low-light intensity, low precipitation, low soil mass and low soil water retention. These results are essential for understanding the ecological adaptation of orchid species in subtropical karst limestone region.