With the automation of surface weather observing system, the observation of wet bulb temperature has been stopped. In order to estimate the wetbulb temperature, the approximation method and multiple regression method are used. Based on the hourly observation data at 134 reference climatological stations throughout China in 2001, as well as those at 75 stations in Hubei Province from 1991 to 2000, the error analysis of two kinds of wetbulb temperature estimation methods is carried out. The results show that: (1) Using approximation method to estimate the wetbulb temperature, its error is very small, and the maximum error is 0.19 ℃; (2) Using multiple regression methods to estimate the wetbulb temperature, the frequency of error within ±0.4 ℃ is over 99%;(3) Different ventilation conditions on the estimation of wetbulb temperature have considerable influences, and they are related with the relative humidity closely. As the relative humidity increases, the impacts of ventilation condition are gradually reduced. (4) Wetbulb freezing on the estimation of wetbulb temperature has no considerable influences.