A fluid heating device of a vehicle fuel system includes: a case having a fluid inlet for letting in fluid, a fluid outlet for letting out the fluid, and an inner space that communicates with the fluid inlet and the fluid outlet; upper and lower power-supply and heat-radiation plates that are arranged in the inner space to be vertically spaced apart from each other, and supply external power; and one or more PTC elements that are interposed between the upper and lower power-supply and heat-radiation plates to receive the external power, and spaced apart from each other to form one or more fluid flow holes. Accordingly, the combustion of the fuel and the cold start performance of the vehicle can be improved.