Using a heated shock tube and an intensified spectroscopic detector CCD, transient emission spectra of n-dodecane in the combustion reaction were measured in the range of 200~900 nm. Experiments were conducted at pressure of 4.0 atm, temperatures of (1 200~1 300) K, equivalence ratios of 0.5, 1.0, and 2.0. Results show that the main emission bands are attributed to OH, CH and C2 radicals produced during the combustion process. In the different equivalence ratios, the emission intensities of OH(306.4 nm)/CH(431.4 nm)/C2(516.4 nm) are significantly different in the combustion process, which indicates that fuel-lean situation is good for generation of OH radicals, and fuel-rich situation is good for C2. Different diluent gases lead to different combustion temperatures when the fuel burns, which causes the different patterns of the emission spectra of the fuel. The variation of OH, CH and C2 radicals produced in the combustion of n-dodecane are shown clearly by the time-resolved spectrum obtained. This research is helpful for understanding the properties and validating the mechanism of n-dodecane combustion reaction.