The extent interline of evaporating region is analyzed for polar liquid film, with the disjoining pressure expressed by Pd= B ln(t) + A. An average effective evaporation is defined for this region and expressed as a simple equation. The results of analysis show that the average effective evaporation rate varies with the relative vapor pressure and so does the length of the interline evaporating region. The increase in relative vapor pressure will make the evaporation from the wetting film more significant.