The butanol-diesel blended fuel possesses broad application prospects in energy industry owing to its excellent properties; thus, studying on flame spread over the blended fuel is of great significance for both scientific meanings and practical guidelines. Several fundamental parameters of flame spread, including the flame spread rate, frequency of flame oscillation, temperature distribution, and velocity of subsurface flow are characterized. Prior to analyzing the experimental data, a blended fuel flashpoint-prediction model is developed based upon Le Chatelier's rule, Antoine's principle, and the ideal liquid evaporation theory. For low ratio of butanol, the calculated values of the butanol-diesel blended fuel flashpoints agree well with those achieved through experimental methodology. The flame spread characteristics of the blended fuel approach those of diesel fuel as the ratio of butanol is less than 17.5%, whereas they resemble those of pure butanol fuel with the ratio of butanol beyond 17.5%. Further, an increase in the ratio of butanol leads to an increase in the flame spread rate as well as the velocity of subsurface flow. The findings of the present work are useful to provide the basic data for butanol-diesel blended fuel spilling fire, and also to develop some fire prevention measures.