Abstract: The calculation and analysis indicte that:(1)The total water content of global cloud is nearly 90×10⁹ t,which is less than 1% comparing with the global vapor.So when calculating the amount of globe atmospheric water,the cloud water content can be ignored;(2)Cumulonimbus is abundant of water,but calculation shows that its precipitable water is less than 3 mm;and(3)There are 1 000 mm water precipitated from the cloud every year,but the precipitable water of cloud is exiguity,so water circulation is very quickly.The duration of a water element from the beginning of cloud to landing as rain is less than 2 hours.