Abstract: The numerical model calculation is conducted on the acidity of cloud water under the assumption that the cloud droplets formed on H2SO4 and other sulfate and nitrate nuclei dissolve acidic and alkaline gases to achieve gas-liquid equilibrium in a very short time. The calculating result shows that the acidification of cloud water is not only related to the initial concentration of acidic and alkakine gases and particulate components in cloud air, but also is related to liquid water content in the cloud.