In 1972 mural paintings of Takamatsuzuka tumulus were discovered and have been conserved on site for 35 years, but fungi growth on the mural paintings was not suppressed. In 2007 the stone chamber was dismantled and removed to the facility for conservation and restoration. The purposes of our study are to clarify the main cause of the deterioration and to propose a suitable method to prevent the deterioration for preserving them on site. In this paper, we developed the two-dimensional analysis model by considering the actual change of the surrounding mound because of the excavation in 1972, and perform the analysis of heat behavior of Takamatsuzuka tumulus before and after excavation and compare effects of different sun-shading methods on heat behavior of the stone chamber. The main results are as follows: (1) after the excavation, the inside surface temperature distribution of the stone chamber and the amplitude of indoor temperature become larger. (2) Using the sun-shading panel in the area of excavation is an effective method to reduce the average indoor temperature; however, it has no influence on reducing the temperature distribution of the stone chamber and the temperature difference between the inside wall and indoor.