Wet bulb globe temperature (WBGT) is the thermal environmental index that acquired the ISO7243 authentication of the international standard system，which is adopted by countries including America, Australia, Japan and China, etc. Currently, the simplified calculation of the outdoor WBGT is mostly summarized or verified based on the actual measurement in low altitude areas. To research on the simplified calculation method of outdoor WBGT for areas with low latitude and high altitude, take Guiyang, a typical city with low latitude and high altitude as an example, then through actual measurement of data including air temperature, solar radiation, relative humidity, wind speed, air pressure and WBGT, etc. of different altitudes in summer, the Pearson correlation analysis and hierarchical regression analysis were conducted. The result shows that: except the wind speed, other four parameters are of linear dependence with WBGT, and can be brought into the regression model. In the hierarchical regression, adding in air pressure cold increase the prediction approach of air temperature, solar radiation and relative humidity on WBGT, the regression model had statistical significanct and the influence that the four independent variables added into the model had on WBGT was also of statistical significance. In the outdoor thermal environment evaluation and actual measurement, adoption of empirical formulas by different regions needed to be verified first, and the high-altitude localities were suggested to consider the air pressure parameters in WBGT calculation model.