Molecular dynamics simulation was used to investigate the permeation properties of a virtual condensable vapor through micropores. A permeation model was proposed to simulate the movement of condensable vapor through a micropore. The model is called "micropore filling phase permeation (MFP),"and the effect of feed gas pressure, pore size and pore size distributions on the vapor permeation properties was examined through model calculations. The observed permeance of ethane-like LJ particles at 260 K, a temperature below the critical temperature of real ethane, decreased stepwise at a specific pressure as the mean pressure was increased for micropores sized 0.8 and 1.1 nm in diameter. Analysis of the adsorption isotherm in the pores and vapor permeation simulations revealed the formation of a high-density liquid-like phase in micropores as the MFP caused a decrease in the mobility of permeating molecules. The model calculations based on the MFP showed qualitative agreement with the simulation results.