Hydrogen is a potential energy carrier that reduces greenhouse gas emissions. The amount of transport of hydrogen is the weakness limiting its large-scale application. Hydrogen blended to natural gas can realize the large-scale, long distance, low-cost transportation for hydrogen. The hydrogen blended natural gas causes change of the flow rate, pressure and so on, then reduce the performance of ultrasonic flowmeter. Therefore, it is necessary to research the mixing process of hydrogen blended to natural gas and natural gas and the adaptability of ultrasonic flowmeter. T-type, one-turn spiral and one-turn spiral combined shrink pipeline model was constructed. The effect of piping structure, mixing hydrogen ratio on the hydrogen concentration and velocity distribution was researched in mixed gas in the flow field using computational fluid dynamics (CFD). The results show that when hydrogen ratio is 5%, the blended pipeline C is the best. Hydrogen mole fraction is about 4.92% when hydrogen and natural gas is blended uniformly. By analyzing the adaptability of ultrasonic flow meters, specific installation locations can be recommend. The research results can provide reference for accurate metering of hydrogen blended to natural gas with ultrasonic flowmeter.