Abstract: The numerical calculation method of transient flow with a little gas (10^-6 < α≤10^-4) content in pipeline is studied in this paper. The ladder integral is adopted to formulate the transient differential equations, which involves the variation of sound speed at different positions in pipeline. To solve the equations, the scheme with slipping nodes based on the method of characteristic is established. In this method, the liquid column separation is considered, and the fixed time step is convenient to calculate with computer.