Carbon membranes were prepared by coating an ethanol solution of phenol-formaldehyde novolac resin with additive on the porous green support from the same material and further heat treatment. The heating process was divided into two steps, stabilization and carbonization. The influences of heat variables including heating rate, stabilization and carbonization temperature on membrane properties were investigated. Pure gas of N2, CH4, and CO2 was used to test membrane permeance. These carbon membranes have good capabilities towards separation of CO2/N2 and CO2/CH4.