Abstract: Transient flow induced by the change of fluid flow rate occurs frequently in two-phase pipelines, therefore it is highly significant to study transient two-phase flows. For the purpose of studying the characteristic of the transient flow initiated by the change of gas flow rate, the experiments of transient flow were conducted on the multiphase flow loop. The transient pressure characteristics are elaborated. After the sudden change of gas flow rate, the pressure waves propagate downstream while the maximum pressure change amplitudes and the change velocity attenuate along the pipeline. Increasing the gas flow rate leads to the sharp increase of pressure and the peak pressure exceeds the steady state value. Near the peak, there exists a short period that the pressure is almost constant. Then the pressure falls and tends to the final steady state. Decreasing the gas flow rate causes the reverse change that takes more time than the process of increasing the flow rate. The transient pressure response in the low liquid flow rate and high flow rate are different. The evolutions of pressure overshoot and undershoot along the pipeline show opposite trend in the two cases.