Abstract: Wet bulb temperatures are an important environmental parameter for construction projects such as HVAC and building design. However, due to various reasons, meteorological stations across China have stopped the manual observation of wet bulb temperature since 2000. In order to solve the problem of the lack of this environmental parameter in the engineering design, this paper not only puts forward an algorithm that uses air temperature, relative humidity and air pressure to quickly calculate the temperature of the wet bulb, but also gives the key part of the algorithm implemented in python language. The comparative measurement shows that the differences between the calculation results and the traditional manual observations remain small, and in most cases the former is consistent with the latter. To be specific, the difference between the calculated results and those from the commonly used traversal lookup method is tiny (< 0.01 ℃). The calculation speed of the proposed method is extremely fast, and in most cases, the result with an accuracy of 0.01 ℃ can be calculated in a 3-step cycle, which can fully meet the calculation needs of the wet bulb temperature in actual work. Finally, the statistical results of the calculated summertime outdoor wet bulb temperature in different years in Ningxia are listed to analyze the main sources of error in calculation results and to offer suggestions for improving the calculation accuracy.