This study investigates the application of an EPS light-gauge steel composite envelope system in rural buildings located in the hot-summer and warm-winter region of Hainan. An experimental building was constructed in Shitang Village, Ding’an County, Hainan Province, using traditional brick structures as a control for comparison. Energy consumption simulations, environmental simulations, and practical experiments were conducted between the experimental building and traditional rural buildings. The results indicated that the relative humidity of the EPS light steel structure building ranged from 55% to 75%, while that of the traditional rural building ranged from 65% to 85%. On sunny days with open windows, the indoor temperature of the EPS light steel structure building was consistently lower than that of the traditional rural building during the day (8:00 AM to 6:00 PM), with a maximum difference of 1.3°C; the temperature variation was less influenced by outdoor temperatures. Additionally, the average indoor temperature at night in winter was 0.7°C higher in the EPS light steel structure building compared to the traditional rural building, indicating superior insulation performance in winter. By utilizing the low energy consumption approach of passive houses, buildings with EPS wall structures can provide a comfortable living environment, which holds practical significance for energy-saving development in rural buildings in Hainan Province.