Using an intensified spectroscopic detector CCD and a chemical shock tube, transient emission spectra of n-heptane during the reaction process of combustion were measured, with exposure time of 6 μs and a spectral range of 200~850 nm. Experiments were conducted at an ignition temperature of 1 408 K and pressure of 2.0 atmos, with an initial fuel mole fraction of 1.0% and an equivalence ratio of 1.0. Measured emission bands were determined to be produced by OH, CH and C2 free radicals, which reveals that small OH, CH and C2 radicals are important intermediate products in the combustion process of n-heptane. Time-resolved spectra indicate that radical concentrations of OH, CH and C2 reached their peaks sharply; however, CH and C2 reduced and disappeared rapidly while the duration of OH was much longer in the reaction. This work provides experimental data for understanding the microscopic process and validating the mechanism of n-heptane combustion reaction.