In order to reduce the safety problems caused by leakage of hydrogen-blended natural gas during the distribution，based on fluid mechanics and porous media theory，a three-dimensional numerical model of leakage and diffusion of urban buried hydrogen-blended natural gas pipeline was established by Fluent software. The effects of hydrogen blending ratio，leakage aperture，pipeline pressure，pipeline buried depth and soil type on the leakage of hydrogen-blended natural gas and the vertical diffusion distance of the lower explosion limit of methane and hydrogen were analyzed. The results show that the larger the proportion of hydrogen blending，the smaller the leakage of hydrogen-blended natural gas，and the longer the time it takes for the methane explosion lower limit contour to diffuse to the surface，while the opposite is true for hydrogen. Secondly，the leakage amount is about twice as much as 5 mm when the leakage aperture is 10 mm. The leakage amount is about twice as much as 10 mm when the leakage aperture is 20 mm. The larger the leakage aperture，the shorter the time required for the lower explosion limit of methane and hydrogen to reach the surface. Thirdly，the greater the pipeline pressure，the greater the leakage of hydrogen-blended natural gas and the faster the diffusion speed，and the higher the risk coefficient. Besides，when the buried depth of the pipeline is 1.1m，the leakage is largest，followed by 1.4 m and 0.8 m. The shallower the buried depth，the shorter the time required for the lower explosion limit of methane and hydrogen to reach the surface. Finally，the soil type has an important influence on the leakage and diffusion of hydrogen-blended natural gas. When the soil type is silty sand，the leakage and diffusion rate of hydrogen-blended natural gas are the largest，followed by loam and finally clay.