N-butanol is a promising alternative fuel for diesel. The study on the self-luminosity spectra of combustion intermediates and flame development in diesel engine cylinder was helpful to understand the influence law of diesel blended n-butanol deeply on the combustion process in diesel engine cylinder. Therefore, this paper used the high-speed flame imaging technology and self-luminosity spectroscopy analysis to study the effects of pure diesel and diesel blending n-butanol on the flame development and self-luminosity spectrum of the engine cylinder on an optical engine. During the test, the optical engine speed was 1 200 r·min-1, with an injection pressure of 600 bar and an intake air heating to 398 K, bringing the temperature around the top dead center to approximately 900 K. Pure diesel, diesel blended with 20% n-butanol fuel and diesel blended with 40% n-butanol fuel were represented by D100, DB20 and DB40 respectively. The injection masses of D100, DB20 and DB40 were respectively 17.5, 18.7 and 19.2 mg per fired cycle to ensure the same engine output. The experiment results show that when the cooling water temperature remains unchanged, with a delayed start of fuel injection (SOI), the ignition delay is shortened, the initial fire nucleus formation time is delayed, the blue premixed flame proportion is reduced; when the SOI remains unchanged, with the increase of cooling water temperature, the ignition delay is shortened, the initial nucleus formation time is advanced, the proportion of blue premixed flame decreases. With the increase of n-butanol blending ratio, the characteristic of the local mixture is first ignited, the ignition time is delayed, the proportion of blue premixed flame increases, and the flame luminosity of fuel decreases. The luminosity of the flame is from D100>DB20>DB40. For D100 fuel, with delayed injection, the peak of the whole spectrum shifts to a larger wavelength direction, soot radiation is enhanced, the peak light intensity of the OH band first increases and then decreases, and the occurrence time of the OH band and the CH2O band is delayed, indicating the high temperature and the low temperature reaction delayed. When the SOI remains unchanged, with the increase of cooling water temperature, the light intensity of whole spectrum increases and the occurrence time of OH and CH2O bands is ahead of schedule, indicating the high temperature and the low temperature reaction advanced. With the SOI delay, the whole light intensity of the spectrum of DB40 fuel after the diesel blended with n-butanol, increases, the peak light intensity of the OH band and the CH2O band increases, which means that delaying injection to DB40 fuel also helps to promote high temperature and low temperature reactions. The whole intensity of the DB40 fuel spectrum is lower than that of D100 fuel, and the occurrence time of OH and CH2O bands appear later than D100 fuel, indicating that both the high temperature and the low temperature reaction of the fuel after the addition of n-butanol are delayed relative to the D100 fuel. Under the condition of SOI-15 and cooling water temperature of 95 ℃, the spectrum of D100 fuel exhibits similar characteristics of the soot blackbody radiation spectrum after 2 ℃A, while DB40 fuel first exhibits the characteristics of CO oxidation continuous spectrum, then the characteristics of the soot blackbody radiation spectrum are exhibited after 15 ℃A.