Abstract: Chemiluminescence has potential for the combustion diagnostics measurements of engines and aero-propulsion systems. This work experimentally and numerically studied the most typical chemistry of chemiluminescence (OH^* and CH^*) formation reactions, as well as the changing law of these excited species with the equivalence ratio and heat release in hydrocarbon fuel flames. (1) The emission of chemiluminescence was quantitatively measured on the methane-air premixed flames by the wavelength-resolved detection system with optical-path-corrected emission calibration method, which can easily capture the concentration of corresponding excited species. (2) The one-dimensional combustion simulations with the experimental equivalence ratios from 0.7 to 1.33 and various rate coefficients for species OH^* and CH^* were conducted. The numerical results of the heat release rate and distributions of chemiluminescence show that the OH^* and CH^* are better indicators than C₂^*, while the CO₂^* distribution has the worst correlation with the heat release. (3) Quantitative comparisons were made for the formation of OH^* and CH^* based on the simulations and experimental results, and then the main formation channels were evaluated for these two species.