Natural gas with H2 is widely used for lean-burn combustion, which leads to NOx emission as the main problem for it. For decreasing NOx emission and increasing thermal efficiency, the investigation on seeking the influence of H2 fractions on the mixture of CH4 and CO2 was conducted. Firstly, the ignition timing was decided through thermal efficiency and brake mean effective pressure (BMEP) for CH4 only. Then, combustion characteristics of CH4, CH4+CO2 and CH4+CO2+H2 were compared with volume percentage of H2 changing from 5% to 30%. Finally, the H2 injection strategy was checked between closed and open valve injections. Among these discussions, thermal efficiency, power output, BMEP and fuel consumption were evaluated. Results show that CO2 addition decreases power output and BMEP, leading to much more fuel consumption and lower thermal efficiency. When H2 is added, at the rich mixture conditions (λ<1.0), power output and thermal efficiency decrease sharply as the mixture is enriched. However, at the lean-burn conditions (λ>1.0), the decrease in flow rate of lower heating value (LHV) and increase in power output finally result in the higher efficiency with H2 addition. Moreover, when λ>1.0, both low fuel consumption and high efficiency can be obtained with H2 addition to achieve the high BMEP. Furthermore, the open valve injection could obtain higher thermal efficiency, power output and BMEP with lower fuel consumption, suggesting that the H2 injection strategy should be well controlled with the ignition timing.