The phase II upgrading project of Hefei 800MeV electron storage ring is being carried out

and its new RF cavity will be finished. In high current operation mode the narrow band coupling impedance of RF cavity can cause different beam bunches to interact

so both longitudinal and transverse coupled modes will be excited. To estimate the effect of the RF cavity coupling impedance on stored bunch intensity fully

the long-range wakefield and the narrow band coupling impedance of RF cavity were calculated with MAFIA program. And the calculation results showed that there are some high order modes in the new RF cavity

which need to be damped.