The liquid superheat limit and vapor subcooling limit in homogeneous nucleation are determined in the present paper by using density fluctuation theory of statistical thermodynamics. Taking water and steam as examples, calculation is performed to predict the superheat limit and subcooling limit of them under different pressure.In conclusion, the mechanism of nucleate condensation of steam is much more complicated than the mechanism of liquid nucleate boiling. It is predicted that the influence of kinetic effects is very important to the vapor nucleate condensation.