In this study, using a droplet dripping and evaporation test rig, over ten thousands droplets of diesel and bio-diesel fuels were dripped on a hot surface repeatedly, and evaporation deposits formed from them were quantitatively analyzed. Results show that wet-dry condition and hot surface temperature were main controlling factors of deposits development. Empirical equations of deposits development were derived from the experimental results. Further carbonaceous evaporation deposits from RME were around ten times serious than diesel fuel. The main reason of it was that bio-diesel fuel was produced from various plant oils through esterification and it was liquid phase chemical reaction process with no hot distillation, so that thermal stability of bio-diesel fuel was poor.