To analyze thermal environment and its effect on worker's thermal adaptation, a field study was conducted in a rubber factory during summer in 2016. The indoor and outdoor environment parameters were tested during investigation and questionnaire surveys were collected. During the survey, 75% of observed indoor temperature fell within the range of 28-32 degrees C. The results show that with natural ventilation, most of the time, the indoor air temperature was high. Most of workers had slightly drafts feelings due to non-uniformly distributed air in the workplace. The estimated clothing insulation was between 0.62 and 0.73clo. Under some negative conditions, such as restricted clothing and poor ventilation, high temperature is still accepted by workers. Analysis of experimental data reveals that PMV was higher than that of TSV. The neutral temperature difference between PMV and TSV is 2.9 degrees C. This indicates that workers in this survey adapt to high temperature environment better than that have been expected by PMV model. A thermal adaptive model is proposed. Compared with other models, it has been found that the slope of this model is larger than the others. This presents that workers adapts to the increasing outdoor temperature more rapidly than subjects in other studies. According to the model, the 90% acceptable temperature ranges from 23.2 degrees C to 32.2 degrees C and the 80% acceptable temperature ranges from 26.3 to 33.3 degrees C. (C) 2017 Elsevier B.V. All rights reserved.