Currently Langmuir adsorption model is used to describe adsorption/desorption effect in the porous flow equation of shale gas. But Langmuir model cannot describe the supercritical isotherm under the reservoir condition, hence the porous flow equation which contains supercritical adsorption model need to be developed. In the paper, we construct a new supercritical adsorption model based on statistic thermodynamics and suitable assumptions, and then the porous flow equation with supercritical adsorption model is built. And we research the difference between the new flow equation and the flow equation with Langmuir model. The results present that: the new supercritical adsorption model can represent the supercritical adsorption isotherm of methane on shale precisely, and the accuracy of Langmuir representing the same isotherm is lower than the precision of the former; comparing to the flow model with Langmuir adsorption model the new seepage model can fit the experiment data with a higher precision and express the adsorption/desorption effect with more clearly.