Abstract: The mixing of hydrogen will increase the leakage and explosion risk of natural gas pipelines. However, the pressure drop rate threshold of existing block valve in natural gas pipeline cannot meet the safety requirements of hydrogen-blended natural gas pipeline transportation. Thereby, the pressure drop rate of the pipeline block valves under the leakage and distribution conditions was simulated and calculated by the SPS software, then a method for setting of the pipeline threshold was developed so that the changing rules of the pressure drop rate of the block valves and its appropriate threshold were gained by simulation under six influencing factors, and further the formulas for the pressure drop rate thresholds of the block valves were formed by fitting for pure gas and 10% hydrogen bending ratio natural gas pipelines respectively. The results show that: after the pipeline leaks, the upstream and downstream pressure drop rates increase with the increasing of the hydrogen blending ratio. The threshold of pressure drop rate increases with the hydrogen blended. The leakage position, pressure and length of the pipelines have great effect on the pressure drop rate threshold, but the flow, the pipeline diameter and the diameter of the leakage holes have little effect on the pressure drop rate threshold. Moreover, the calculated results of the threshold fitting formula are in good agreement with the simulation results. So, the research results could provide theoretical guidance for improving the intrinsic safety of the hydrogen-blend natural gas pipeline.