An elaborate cloud chemistry box model hasdeveloped in which gaseous-phase photochemistry iscoupled with aqueous-phase chemistry to investigate thevariation of ozone concentration and its distributionfeatures above and below cloud, and in its upper andlower part, with results compared to observations. Thecloud chemistry model is composed of three parts:gaseous-phase chemistry, aqueous-phase chemistry, andscavenging of soluble gases. The cloud influence on theozone concentration can be separated into three portions:1) the change of solar radiation flux by cloud which isresponsible for decreasing or increasing of photochemicalreaction in the troposphere and thus reducing orenhancing the concentration; 2) direct absorption ofozone and its precursors (NO ₓ, NMHC,free radicals, etc.) by in-cloud liquid water; 3)aqueous-phase chemical reaction happening to speciesabsorbed by cloud, responsible for the change in gaseous-phase ozone concentration. Numerical simulations showsubstantial difference in the importance regarding theeffect of these factors on ozone between these levels anda close relation of cloud physical structure to thefactors. The results agree well with the observations.