The ecological experience of traditional regional architecture provides an excellent reference for coping with increased energy consumption from cooling in tropical developing countries. However, the thermal comfort of traditional architecture and the effectiveness of its passive measures still need to be further verified in summertime conditions in hot and humid regions. In this study, we selected the traditional Li architecture, including boat- and Kim-shaped houses, for thermal environment tests. Subsequently, we analyzed the operative temperature and PMV-PPD index to determine their indoor thermal comfort and major passive strategies under hot summer conditions. Finally, we propose suggestions for improving the deficiencies of existing passive strategies. Our results show that the traditional Li architecture failed to satisfy indoor thermal comfort for more than half of the test time during the summer. Gable bottom openings and entry door ventilation can increase indoor ventilation with negligible increases in heat gain; however, existing ventilation efficiency is too low to substantially improve indoor thermal comfort. Additionally, we found that the evolution from boat- to Kim-shaped houses was not fully compatible with the significance of climatic adaptation. Kim-shaped houses benefited from the change in the envelope and external environment and its indoor moisture dissipation rate was accelerated; however, their eave shading made the wind speed attenuation more remarkable between indoor and outdoor. These results can help improve the indoor thermal comfort of traditional architecture in hot and humid regions.