Abstract: An acoustic emission testing system for pressure pipeline was constructed with seamless steel pipes, reducers, elbows, tees, flow meters, pipes with cracks, and acoustic emission detector etc. The experiments were carried out with the system. We analyzed the relationship between the loading pressure and the weld crack activity of 20 steel pipe, and we found out the impact of the media would not cause a continuous acoustic emission signal on the reducer and the elbow in the case of low flow velocity. The study provided reference for the field application of pressure pipeline acoustic emission testing.