Abstract:Two national second-class protected plant species, Calocedrus macrolepis and Pseudotsuga sinensis are mainly distributed in Yimen County, Yunnan Province. These two species and two communities dominanted by Calocedrus macrolepis and Pseudotsuga sinensis respctively are believed to be very valuable in conservation. They have become the first nature reserve in China focusing on the conservation of these two species only. The study on the characteristics of community, its floristic constitution and the population composition of these two species shows the urgency of conservaation.The natural distribution has been limited because Calocedrus macrolepis is a shade tolerant tree while Pseudotsuga sinensis is shade intolerant. Calocedrus macrolepis is regarded to be originated from the central and central-southern part of Yunnan based on fossils evidences. The habitat of Calocedrus macrolepis tends to prefer a more tropical climate than that of Pseudotsuga sinensis based on the analysis of distribution patterns of genera of seed plants in two communities. The above statements provide a theoretic foundation for in situ and ex situ conservation of these two species.