Abstract: In order to find the characteristics of gas flowrate increasing transient under the slug flow regime,a statistical investigation was carried out in a 378 m long, 80 mm i.d. stainless steel pipeline. Air and water were used as test fluids and responses to change of gas flowrate were measured by using a series of pressure transducers. Differential pressure signal was obtained by subtracting downstream pressure signal from upstream pressure signal.According to the test results, the development trends and statistical characteristics of pressure and differential pressure along the pipe during the transient process of gas flowrate increasing was analyzed.An equation for the calculation of pressure overshoot was proposed for this transient process.