Hydrogen is a carbon-free energy resource which can be produced from a wide range of sources, and hydrogen blending is a transitional stage in the shift from natural gas to hydrogen systems. However, the introduction of hydrogen has also raised widespread safety concerns. This paper uses Fluent numerical simulation software to simulate the leakage of hydrogen-blended natural gas in the kitchen to analyse the concentration distribution and its variation pattern after the leakage. An experimental platform was set up to carry out the leakage experiments and a mixture of nitrogen and helium gas was used instead of hydrogen-blended natural gas for the simulations and experiments. The simulation results showed that the leaking gas spread and accumulated towards the top of the space, gradually filling the entire area as the leak continued. As the proportion of hydrogen blending in the leaking gas increased, the diffusion capacity of the gas in the confined space increased. As the flow rate of the leaking gas increased, the average level of leaking gas concentration increased and the gas stratification in the confined kitchen diminished. The experimentally measured gas concentration distribution agreed with the Fluent simulation results. After demonstrating the feasibility conditions of the model, the diffusion of hydrogen-blended natural gas in the kitchen was further simulated. It was concluded that blending hydrogen into natural gas would promote the diffusion of the gas after a leak, and the gas would be more widely distributed in the kitchen, resulting in an increased risk in the event of a leak.