In urbanization, prefab buildings for office use are extensively applied on construction sites due to its convenience and flexibility. In order to study the adaptive thermal comfort in prefab construction site offices (PCSO),combined thermal parameter measurement and questionnaire survey were conducted on selected construction sites in Guangzhou during summer and winter seasons. 1179 valid questionnaires were collected. The relationship between Predicted Mean Vote (PMV) and the thermal sensation was studied; thermal comfort zones and preferred temperatures in summer and winter seasons were identified. The results show that the indoor thermal environment of the PCSOs was always unacceptable for occupants in summer. However, the percentage of acceptability is much higher in winter. The comfort temperatures in summer and winter are 26.2 °C and 21.1 °C, respectively. In summer, the upper limit of the acceptable temperature is 29.3 °C, and the comfortable temperature range is from 25.0 °C to 28.2 °C, which is different from the thermal comfort zone of ASHRAE–55. An adaptive thermal comfort model for PCSO is established, which is beneficial for reliably evaluating the indoor thermal comfort of PCSO in Guangzhou and other locations with similar environmental conditions.