The effects of fuel types on the soot evolution are studied using laser-induced incandescence (LII) and laser-induced fluorescence (LIF) technologies. The diffusion flames from methane, ethylene and propane are selected as research objectives, and the two-dimensional distributions of volume fraction, primary particle size, and particle number concentration of soot as well as the relative concentration of polycyclic aromatic hydrocarbon (PAH) are measured. The measurement results show that the carbon conversion factors in methane, ethylene and propane flames are 0.0058, 0.144 and 0.043; the average particle sizes of soot are 9.2, 20.8 and 14.7 nm, and the corresponding particle number concentrations are 6.9×10 21, 8.7×10 21 and 7.8×10 21 m -3, respectively. It is found that the PAH and soot formation are fast in the flame for the fuel with the unsaturated bond or more carbon atoms. The comprehensive changes in both specific surface growth rate and growth time for the soot result in the largest soot particle size in ethylene flame and followed by the propane flame and methane flame.