This paper presents the spatial distribution characteristics of a polycyclic aromatic hydrocarbon (PAH) fluorescence signal in a propane-air diffusion flame and the variation of time-resolved signal with the flame height position. Results show that the PAH for smaller rings gradually shifts toward larger rings and then toward soot particles with an increase in the flame height position, which demonstrates the formation and growth process of PAH and soot in the combustion. Based on the measurement of time-resolved fluorescence, it is found that in the same environment, the measured fluorescence decay times of larger PAH are longer than those of small PAH for which fluorescence emissions are at shorter wavelengths. As the flame height position increases, the fluorescence decay time is observed to decline owing to the increasing temperature.