The simulation results used the CHEMKIN/PREMIX code to explore the combustion characteristics of n-heptane/hydrogen/air flame. The initial temperature is set as 300 K, the pressures are set as 1, 2, 5, 10, and 20 atm, and the equivalence ratios are set as 0.8-1.4. This research mainly focuses on the characteristic of flame, radicals, and temperature sensitivity of the H radical. The results show that the simulation results maintain the consistency of the experimental results, and other mechanism simulation results and the tendency are same. The changes of laminar burning velocity (LBV) are obvious when hydrogen (H-2) is mixed, but the influence of H-2 addition on adiabatic flame temperature is greater slightly than that on LBV. The sensitivity analysis of the H radical shows that the release of the H radical will compete with n-heptane for oxygen when the H-2 doping ratio is increased. With the pressure rise, the chemical reaction of H2O strengthens the inhibition of H sensitivity. Hydrogen addition does not change the main reaction of hydrocarbon fuels. H + O-2 double left right arrow O + OH and H2O + M double left right arrow H + OH + M are also the exothermic reaction and endothermic reactions, respectively, which are the uppermost.