At Venus's cloud top (~70 km) the SO2 scale height HSO2 is one of the important observational quantities to give us scientific information about not only the vertical distribution of SO2 but also the chemical and transport processes of SO2. HSO2 is controlled by the SO2 photodissociation rate and by the concentrations of ClO and SO2 through the SO2 oxidation in the sulfur cycle including the SOx-ClOx catalysis. The sensitivity of HSO2 in the SOx-ClOx process is classified into three regimes: inefficient-oxidation, low-ClO, and high-ClO regimes. On the other hand, the sensitivity of HSO2 to the SO2 oxidation and the vertical flow is also classified into three regimes: regime O, where HSO2 is controlled by the SO2 oxidation, regime D, where HSO2 is controlled by the downward flow, and regime U, where HSO2 is insensitive to both the SO2 oxidation and the vertical flow. As a result of exploring the sensitivity of HSO2 in the chemical and transport processes, either strong downward flow or some other SO2 oxidation process in addition to the SOx-ClOx catalysis is required in order to reproduce the small HSO2 observed at high latitudes. ¿ 2001 American Geophysical Union