Mixing hydrogen into natural gas pipelines for transportation is an effective way to achieve large?scale,long?distance, and low?cost transportation of hydrogen.However, the mixing of hydrogen will have a great impact on the hydraulic characteristics and safety of natural gas pipeline during transportation.In this regard,SPS software was used to simulate the transportation and leakage conditions of natural gas pipelines with different hydrogen mixing ratios, in order to investigate the effects of hydrogen mixing on the hydraulic characteristics of natural gas pipelines,the operating characteristics of centrifugal compressors,and the pressure drop rate of block valve and leakage after leakage.The results show that adding hydrogen will reduce the gas transmission efficiency of the natural gas pipeline network and compressor performance,which can be compensated by increasing the pressure drop.The dynamic pressure amplitude decreases with the increase of hydrogen mixing ratio under the same natural gas output.When the hydrogen mixed natural gas pipeline leaks,the pressure drop rate and the leakage would increase as the increasing of hydrogen mixing,and the set value of the pressure drop rate threshold of the pipeline block valve also increases accordingly.In conclusion,the research results in this work can provide the basis for the research on determining the maximum of hydrogen mixing ratio in the natural gas pipeline and provide a reference for the determination of hydrogen mixing transportation technology in natural gas pipelines.