The concept of the wetting loss of a raingage and the factors affectting the wetting loss are introduced.The amount of the wetting loss of the standard gage of China has been determined after the analysis of the data of wetting loss, which have been collected by the wetting experiments with a gage and the observations in natural conditions. And the wetting losses in the precipitation measurement in the area of the head of Wulumuqi river in summer have been corrected.