The sol-air temperature is a hypothetical parameter to reflect the outdoor multi-field coupled thermal environments of air temperature, solar radiation, and long-wave radiation. The simplified model was proposed in code for thermal design of China which ignores the influence of long-wave radiation of sky and surrounding environment. However, the climate is characterized by strong radiation, high temperature and high humidity in tropical islands, and the underlying surface types are mostly sea surface. This may affect the applicability of sol-air temperature models. To explore the above issues, the Davis weather station and Kipp & Zonen solar radiation observation system were used to gather the meteorological and radiation data around the building, which is a case study building near the coastline in Sanya. Also, the dynamic temperature of the external surface of envelope and sea surface was captured. Then, the weather types were classified by clearness index, and the influence of sky and sea surface radiation on the sol-air temperature calculation of each orientation in different sky conditions is analysed. The results show that the sol-air temperature decreased by 1.07-2.44 ℃ on average considering the long-wave radiation of the sky and sea surface, especially in clear sky, with an average decrease of 1.49-3.85 ℃.