Abstract: The propagation characteristics of pressure wave in gas flowrate transient air-water slug flow is firstly investigated by improved slug tracking model. The development tendency of pressure wave along the pipe line and the efficiency which liquid flowrate and the variation of gas flowrate affect the speeds of pressure wave propagation are primarily analyzed. And the model results are compared to the experimental ones, whichare gained in 380 m long, 80 mm i. d. horizontal stainless steel pipeline. The results indicate that the model can effectively simulate the propagation characteristics of gas flowrate transient pressure wave, that the speeds of pressure wave propagation will be attenuated along the pipeline, and that the attenuation velocity of the speeds of pressure wave propagation in gas flowrate increasing slug flow will decrease along the pipeline.