Transporting hydrogen?blended natural gas (HBNG) through existing natural gas pipelines can significantly reduce the cost of hydrogen transportation. To evaluate the risk of HBNG pipeline leakage, a high?pressure pipeline small?hole leakage model and a Gaussian plume model are combined, taking into account the lifting height caused by the initial momentum of the jet. The calculation results of the Gaussian plume model are compared with the existing experimental data. Then, the influence of the hydrogen mixing ratio, pipeline pressure, wind speed, and leakage hole diameter on the explosion risk area caused by the leakage of the natural gas pipeline is analyzed. The research results indicate that the calculation results of the Gaussian plume model are in good agreement with the experimental data. The hydrogen mixing ratio is approximately linearly negatively correlated with the maximum distance from the methane hazardous area, and linearly positively correlated with the maximum distance from the hydrogen hazardous area. The maximum distance between methane and hydrogen hazardous areas is approximately linearly positively correlated with pipeline pressure, negatively correlated with wind speed, and approximately proportional to the diameter of the leakage hole.