The gas flow characteristics are studied of the pipeline of the gas bearing testbed, especially the pipeline velocity and pressure changes. By using the method of characteristics, the flow field was calculated by simplifing the model to onedimensional （1D） nonsteady flow. The calculation results show that the model is able to calculate the flow characteristics of the pipeline nonsteady flow of constant pressure vessel. Method of characteristics can satisfy the requirements of accuracy and computation speed. The study result provides a possible approach for the further design, reliability assessement and optimization of the testbed.