In this study, the body metabolic rate of 10 volunteers performing light, medium and heavy physical labor was examined under different climatic conditions in a chamber. The climatic conditions referred to one group of comfort environment (25 degrees C dry bulb temperature and 50% relative humidity) and three groups of thermal environment (30 degrees C, 35 degrees C, 40 degrees Cdry bulb temperature and 90% relative humidity). The results reveal that for the same labor intensity, the human metabolic rate increases with the rise of environment temperature in the scope of 30 similar to 40 degrees C, 90%RH. The impact of environment temperature on metabolic rate increases with the rise of labor intensity. In addition, the classification of physical labor intensity upgrades when the environment temperature exceeds a certain threshold