A 3, 3, 4, 4-oxydiphthalic dianhydride-4, 4-oxydianiline (ODPA-ODA)-type polyetherimide was modified by blending ethylene glycol (EG) for preparing precursor of freestanding pyrolyzed membranes. The thermal stability, surface elements, microstructure and solubility of modified membranes were investigated by the techniques of thermogravimetric analysis, infrared spectroscopy, X-ray photoelectric spectroscopy and X-ray diffraction, respectively. Results demonstrate that EG can effectively adjust the microstructure and property of the present polyetherimide membranes. As the usage amount of EG elevates, the microstructure of modified membranes tends to become more compact and amorphous. The gas permeability and selectivity of finally derived pyrolyzed membranes exceed 8000 Barrer for H-2 and 17 for H-2/CO2, respectively.