Electron transport parameter is the foundation for revealing the mechanism of corona discharge, and the analysis of electron transport parameter greatly promotes the scientificity and accuracy of prediction on electromagnetic environment that determines engineering cost and environmental protection issues. The influence of humidity on the transport parameters, difficult to ignore, is vague and is rarely studied. In this paper, as the basis for calculation, the collision cross sections of H2O are discussed. Combined with the METHES and the LXCAT database, the electron transport parameters of humid air are completely calculated. By comparing the prediction on the corona onset voltage of a positive conductor, the electron transport parameters gained in this paper show higher accuracy. Finally, the influence of humidity on corona onset voltage is given and then analyzed, which shows good consistency with the results of electron transport parameter and experiment. Further research on the method utilized in present work could contribute to achieving accurate prediction on electromagnetic environment under the combined action of complex environments.