Heat pipe is high performance heat transfer equipment，in order to reduce its complexity in the process of theoretical research，it is necessary to make some simplification.Aiming at the applicability of some basic hypothesis，a one-dimension evaporation-condensation model is proposed.Through primary integration，the governing equations are simplified and the numeric result is got，which indicates that there exist obvious boundary layers in the temperature，velocity and pressure fields in the evaporation and condensation phase interface，and it is more obvious in the evaporation phase interface，where the velocity and pressure have large gradient.When Reynolds number is large enough，the gradient of temperature is large too.From boundary layer phenomenon，a deduction is derived，thermal short-circuit effect，which means the ultimate state of the vapor will be such that the temperature is uniform，the vapor is saturated，and its thermal resistance is zero.