The pore throat structure of low permeability tight sandstone gas reservoir is complex. It is difficult to characterize the flow and distribution of gas and water in it. Based on real low-permeability sandstone core, micro-CT scanning technology was used to construct three-dimensional digital core of the reservoir. Connected pore structure was extracted and unstructured tetrahedral mesh model was established. With level-set method and N-S equation, a mathematical model of gas-water two-phase flow is established which is solved by finite element method. Water drive gas process, residual gas distribution, influence of rock wettability on two-phase flow in low-permeability sandstone gas-water two-phase flow, and interflow characteristics in parallel channels are studied. It shows that level-set method provides clearly gas-water two-phase distribution and migration of the displacement front. Rock wettability has great influence on two-phase flow process, and production degree is higher under water-wet conditions. Interflow phenomenon is obvious in parallel channels. Water phase in the large channel breaks through first and forms a dominant flow channel, while flow in the narrow channel is affected by capillary phenomenon and has great additional resistance.