The factors dramatically influencing thermal comfort usually involve air temperature, radiant temperature, air humidity, air velocity, clothes insulation, and metabolic rate. However, under some special conditions, e. g., altitude environment, the air pressure should be taken into account. Exposure to altitude tends to produce deterioration in human heat diffusion performance, rate of convective heat transfer decreases, and rate of convective heat transfer increases with altitude, energy balance between human body and environment is different from in the normal conditions. In the experiments, thermal perception of 20 test persons (240 person-times) was observed by subjective questionnaire in a simulated hypobaric chamber where the air parameters were controllable. The temperature was set at 22 degrees C, and the barometric conditions were set at 1, 0.95, 0.9, 0.8 atm of simulated hypobaric conditions, corresponding altitude of 0, 400, 800, 2,000 m, respectively. Experiments solved the metabolic rate raised with pressure drop, and the measured PMV differed from actual thermal sensation votes in hypobaric conditions. Moreover, the falling barometric pressure leads to decline in alveolar oxygen, a variety of adaptive physiological processes for oxygen delivery, human metabolism, and thermoregulatory responses as well as thermal perception change. However, the present thermal sensation models were built in the normal environment and there were many divergences in conclusions. Combined with the experiments, this article builds the thermal sensation estimating model under the hypobaric conditions by principal component analysis. The purpose of this study was to make clear whether hypobaric exposure will affect people's thermal sensation and maybe helpful to establish the indoor thermal comfort criterion in the hypobaric environment.