The separation of H-2/CH4 mixtures is very common in the natural gas and petrochemical industries. There are some higher C2-C4 hydrocarbons and water vapor that are used as impurity gases. Si-CHA zeolite membranes display a high H-2 permeance of 1.44 x 10(-6) mol/(m(2) s Pa) (permeability of 10800 barrers) and H-2/CH4 selectivity of 85 for an equimolar H-2/CH4 mixture at 298 K and 0.2 MPa pressure drop. A third gas decreased H-2 permeance and H-2/CH4 selectivity of the membrane. Hydrogen permeance was reduced in an order similar to the adsorption amount in zeolite: H2O > C3H8 > n-butane > ethane. The effects of temperature, pressure, and feed concentration were studied on separation performances of the membrane in the binary and ternary mixtures. A simple model was built up to predict the reduction of permeance and selectivity when multi impurities were contained, and the predicted value agreed well with the tested one. A stable performance was obtained within several hours in all the tests. The separation performance of the membrane was recovered to the original level when the impurity gas was removed.