Abstract: Once the elbow of the middle and low pressure natural gas pipeline in urban areas is damaged, the consequences will be serious and the repair process is complex. In order to monitor, locate and maintain the leakage of urban pipelines better, the flow field and sound field of the leakage at the elbow of middle and low pressure pipeline were studied in this paper. The elbow is simplified as a bent pipe, and the softwares are used for simulation. The structure grid is divided in ICEM, the flow field is analyzed by Fluent, and the pulsating data is introduced into the Virtual.Lab Acoustics for acoustic analysis of the leakage pipe. Then, the elbow hole leak test bench was established, and the simulation results were compared with the experimental results. It is shown that the flow of gas at the leakage hole is complicated and the flow direction is diverse. The energy of the leakage wave is mainly concentrated below 10 Hz, and the sound pressure level rises with the increase of the pipeline pressure. And the sound is mainly sourced from the quadrupole in the jet area and the dipole in the leakage hole wall. The research results provide the reference for the development and safe operation of urban natural gas pipelines.