Abstract: The Monte Carlo method was employed to investigate the effect of critical solvents acetone and heptane on the desorption and extraction of methanol from porous media. The effect of molecular structure of the solvents and extrinsic factors (pore size) on the methanol synthesis process were all took into account when the model was built up. The results showed that polar acetone was beneficial to the desorption of methanol, however the effect of nonpolar heptane on the extraction of methanol was more evident. The effects of the solvents on the desorption of methanol were increased with increasing of the pore size while the effects on the extraction of methanol in the pores were decreased with increasing of the pore size.