Abstract: The proportion of renewable energy power generation in China has increased year by year. As renewable energy power generation, such as wind power and photovoltaic, is characterized by volatility, intermittency, and stochasticity, traditional thermal power units need to be highly flexible while deeply peaking to improve the capacity of renewable energy consumption. In this study, a hydrogen co-firing system for peaking power plants with hydrogen production from renewable energy is proposed. The schematic design of the system is carried out with a 350 MWe thermal power unit as an example, the technical economics of the system with different hydrogen blending ratios andpeaking loads are investigated. Then the impacts of the coal price, carbon tax, and hydrogen production tariffs on the electricity cost per kWh of the peaking plant are analyzed, and the payback period of the project is discussed. The results show that further deep adjustment of boiler load after hydrogen co-firing with an appropriate ratio has better economic benefits. If carbon tax and hydrogen production tariffs are not taken into account, and the coal price is calculated according to 800 yuan/t, the electricity cost without hydrogen co-firing （Scenario 1）is 0.347 yuan/kWh. Further deep adjustment of the boiler load to 20%THA after assisted comsbution with 20% hydrogen co-firing （Scenario 5） would control the electricity cost at an increase of 2.0%. When the coal price rises to over 1 800 yuan/t or the carbon tax rises to over 400 yuan/t, the benefits of hydrogen co-firing in thermal power units in terms of coal saving and carbon reduction become increasingly significant, and the retrofitted scenarios start to dominate in terms of electricity cost per kWh. When the coal price is 1 000 yuan/t and the carbon tax price is 100 yuan/t excluding the hydrogen production tariff, the payback period of Scenario 5 is the shortest, which is 10.65 years. If the coal price and carbon tax increase in the future, the economic benefit of hydrogen co-firing in thermal power units will be more significant.