Occupants’ thermal comfort and their adaptation behaviors are essential aspects of building design and energy operation. There is a growing need to better understand the impact of seasonal variation on occupants’ dynamic thermal comfort which provides evidence for building energy flexible design and management. The aim of this study is to investigate the interaction between occupants’ thermal sensation and adaptive behavior in office buildings. Such understanding can provide detailed adaptation rules of human behavior in dynamic office buildings and quantify energy demands. In this study, a framework of a tracking method is proposed, which combines data collection (continuous monitoring of environmental parameters and daily questionnaire surveys), time boundary division and data analysis. Using the tracking method, field surveys were carried out in three mixed-mode office buildings in Chongqing, China. The time-series data was analyzed based on the indoor operative temperature under free-running conditions and five seasonal periods are classified i.e. Latter Spring (LS), Early Cooling period (EC), Middle Cooling period (MC), Latter Cooling period (LC) and Early Autumn (EA). Results show that for the same outdoor temperatures in different seasons, occupants’ clothing insulation varied, indicating that the occupants were more sensitive to environmental changes in EA than in LS, as well as in EC than in LC. The study that flexible energy operation based on the thermal comfort demand can achieve energy savings compared with fixed temperature.