Research conclusions :(1) The water - binder ratio of the air –tightness concrete should be less than 0.4， no bigger than 0. 45. (2) The silt content of the fine aggregate should be not more than 2.5%. The silt content of the coarse aggregate should not be more than 40 mm，with maximum grain size of no more than 40 mm. (3) The elongated flaky particle content of the coarse aggregate should be strictly controlled，and the ratio of the sand and the aggregate should be more than 36%，and the ratio of the sand and the aggregate should be big as much as possible if allowable. (4)The binder content of the air - tightness concrete should be more than 380 kg for 1 m3 concrete. (5) The silica fume and fly ash are good for improving the air tightness of the concrete. (6) The water reducer and compacting agent are able to improve the air tightness of concrete. When many additives have to be used， their adaptabilities should be tested to make them adaptable each other for obtaining the best air tightness. (7) The C-S-H alkalinity of the cement hydration product can be decreased and compactness can be increased by using silica fume and fly ash. In this way，the directional arrangement of Ca ( OH) 2 at the aggregate interface can be improved, the production of ettringite can be reduced and the air tightness of concrete can be enhanced. (8) The research results can be used in preparation and constmction of air tightness of concrete for the gas tunnel.