A fuel filling apparatus and method for a bi-fuel vehicle using both gasoline and liquefied petroleum gas (LPG) as fuel are provided to an LPG fuel tank. The fuel filling apparatus and method are capable of temporarily burning a portion of LPG fuel after collecting a fuel portion, using a gasoline fuel tank and a canister, when the internal pressure of the LPG fuel tank in the bi-fuel vehicle is equal to or greater than an LPG filling pressure of a filling gun. Additionally, the internal pressure of the LPG fuel tank is decreased to a level below the LPG filling pressure of the filling gun, thereby achieving smoother LPG fuel filling of the LPG fuel tank by the filling gun.