A method for improving a change of fuel in a bi-fuel vehicle includes: a step of measuring an LPG level in an LPG fuel tank; a pressure reference driving step of continuing the driving of the vehicle using the LPG fuel; a pressure change rate reference driving step of continuing the driving of the vehicle using the LPG fuel when it is determined that the vehicle may be driven by the LPG fuel by comparing an LPG rail pressure change quantity and a pressure change quantity in the LPG fuel tank with a set reference value; and a fuel expanding step of continuing the driving of the vehicle using the LPG fuel when it is determined that the vehicle may be driven by the LPG fuel by comparing an injection quantity of LPG fuel and an accumulated value of mileage with a set reference value.