The purpose of this study is to clarify the effects of change of architectural style and open time of the openings on indoor thermal environment in the traditional vernacular house of Taketomi Island. The comparison measurement of indoor thermal environment and CFD analysis of cross ventilation performance in traditional vernacular are conducted. The following results were obtained: 1) When the traditional opening pattern (opening during the day, closing during the night) were reproduced in old Yonaguni house which leaves a traditional architectural style, SET* in the daytime became low about 2°C as compared with the other repaired traditional vernacular. Indoor wind velocity contributed to the fall of the effective temperature most. 2) When openings are closed in old Yonaguni house at night, since the airtight performance of the sashes are low and there is also almost no internal load, SET* also becomes low about 1-2°C at night comparing with other vernaculars. 3) According to CFD analysis, in existing traditional vernaculars, since opening area is halved with the installation of aluminium sashes or podium, PFR/Vp and kinetic energy KE are falling to about 25% and 50% respectively through all wind directions, comparing with the old Yonaguni houses. Especially, the influence by installation of aluminium sashes is larger than that of podium.