In order to explore the mechanism of fuel droplet impacting on a wetted surface in a small-size combustor of diesel engine, experiments and numerical simulation were carried out. High speed camera was used to observe the phenomenon of spreading, liquid sheet formation, breakup and splashing during droplet impact. The results showed that the spreading factor and velocity were closely related to impact velocity. The higher impact velocity droplet had a larger spreading factor, and the intial spreading velocity was the largest, which could be increased by increasing impact velocity. The numerical simulation was developed using volume of fluid method including heat transfer and contact resistance. The mechanism of droplet fluid and heat transfer as well as breakup during impact were obtained according to analysis of results. The numerical results also showed that the pressure gradient inside liquid was the main factor resulting in droplet spreading, liquid sheet formation, breakup and splashing. The capillary wave resulted in the shrink at the neck of the liquid sheet and breakup and splash from the liquid sheet.