Abstract: Evaporation is first discussed on ocean surfaces in tropical zone,finding that evaporation-vapor gone to air will change its surface pressure field,and that the process of the evaporation,s latent heat is composed of the internal latent heat (vapor internal energy) and the external latent heat (vapor pressure energy).The former becomes atmospheric heat energy at once and the latter does work to the atmosphere immediately,thus raising its potential energy.Then,it is the direct role that transforming surface pressure field (or upper geopotential height field) is studied of condensation-precipitation in large-scale flow and cumulus convection.Knowing that Kuo,s method of the parameterization of cumulus convection has embodied the role with the condensation's internal latent heat to warm the atmosphere,this paper suggests that the other role must be considered with the external latent heat to alter upper geopotential height as well as surface pressure,or to do work,following condensationprecipitation taking place in the atmosphere.It is further discussed that distinguishing between convection and non-convection precipitations is that two condensation's external latent heat processes are different.The former is that the ambient air does work to the compensation downdraughts and produces kinetic energy to itself with pressure-gradient force,which would make the convective precipitation organized and become a positive feedback system,but the latter is so called non-convective motion,which usually is large-scale stable precipitation and has no air downdraughts to be done work.But both types of precipitations cause their surface pressure cutting down as well as upper geopotential height to be lower,because vapor condensation's physics mechanism leading to precipitation unigue.Through calculating the reversible and irreversible saturation-adiabatic processes in the atmosphere,in this paper are discussed that the different physical roles of the vapor condensation's internal and external latent heat,and that their different physical roles in two sets of precipitation weather systems:convection and nonconvection.The facts are that the external latent heat is doing negative work in both the reversible and irreversible saturation-adiabatic processes,because a lot of vapor transforms to water in the saturation-air whose vapor pressure energy is reduced.Finally,with the vapor condensation,s external latent heat,the ambient air does work to both types (convection and non-convection) of precipitation weather systems,one kind is hail squall,tornado,tropical storm and typhoon,the other kind is different frontal surfaces.Their diabatic heating efficiencies of the above two types of "doing work engine" are both about 5%.