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Tsugeyama Tumulus is an 88 m keyhole-shaped tumulus located in Takatsuki city in Osaka prefecture. Two stone chambers, which have not been looted, were discovered in the circular portion of the tumulus in 2002. The tumulus was designated as a national historic site in the same year and became subject of permanent preservation. However, in the photo image survey of the stone chamber in 2006, condensation and fungi growth were found. Human bones and funerary goods such as mirrors, on the reverse sides of which designs of gods and animals are carved, are threatened by the impact of condensation, fungi and other factors. Thus, a method for taking out the funerary goods by excavation has been investigated as a workable alternative to continuing preservation on site. During excavation, construction of a shelter and installation of an air conditioning system seemed to be essential because of the risk of progressive deterioration due to drying or occurrence of condensation on excavated artifacts. In this study, we aimed to clarify the proper method of controlling temperature and humidity around the stone chamber. We clarified the principle for controlling air conditioning and investigated the results of numerical analysis considering heat and moisture transfer in the stone chamber and its surrounding ground. One of the main results is that in order to keep temperature in the stone chamber constant and reduce temperature distribution during excavation, it is necessary to maintain a constant temperature and humidity of the space adjacent to the stone chamber and not to insulate the walls of the space. In the future, we plan to propose a method to control temperature, humidity and air quality so that they will be good for the conservation of the funerary goods and the health of the workers when they enter the stone chamber.