In order to explore the influence of butanol on engine combustion, engine visualization experiment was conducted with the mixture of toluene standard reference fuel (TPRF) and various butanol isomers. On a direct-injection ignited optical engine, the high-speed photography and in-cylinder pressure testing was conducted to process and analyze flame images of different TPRF/butanol fuels and a combustion analyzer was used to test the combustion performance of engine. The test results show that the flame velocity and flame area expansion rate are the highest for the blends of n-butanol and TPRF and are the lowest for the blends of tert-butyl alcohol and TPRF. Moreover, the addition of butanol will inhibit the ignition tendency of TPRF, and the combustion duration and ignition delay hence prolong. The prolonging effects from small to large are tert-butyl alcohol, sec-butyl alcohol, isobutyl alcohol and n-butyl alcohol. Besides, the mean effective indicated pressure of engine decreases after blending with butanol due to the lower calorific value, higher viscosity and vaporization latent heat of butanol.