This paper begins with presenting the features of variation on the stable isotope in the atmospheric water vapor and precipitation under the equilibrium and non-equilibrium conditions. The condensation and evaperation are two important progresses of the isotope frac tionation. Generally

it is assumed that the condensation of water vapor in cloud belongs in the equilibrium process (relative humidity=100％)

and the evaperation on the ocean does the non-equilibrium one (relative humidity<100％)

but the evapotranspiration on the ground does not produce the isotope fractionation. The factors influencing the isotope frac tionation include: the transfer of water vapor from source

the condensation temperature

the environmental conditions

the precipitation

the height above sea-level and the distance to the open seas and so forth. All of these affecting factors are variable with the space and time. At last the foundations about the isotopic application on the study of the ice core and the probable climatological interpretation on the isotopic variation in the ice core are shown.