Abstract: A parameterized model of microphysical processes in cumulonimbus clouds is presented.The change rates of the water contents of vapor and cloud dropplets,water contents and number concentrations of ice crystals,graupels,hails and raindrops are deduced for 26 microprocesses which include condensation deposition,evaporation,collection,riming,freezing,melting,nucleation and multiplication of ice crystals and autoconversions of cloud-rain,ice-graupel and graupel-hail.