An apparatus for controlling fuel injection of a bi-fuel vehicle running on gasoline and liquefied petroleum gas, the apparatus comprising: an engine using gasoline and LPG as fuels; a gasoline driver comprising a gasoline fuel pump and a gasoline injector; a liquefied petroleum injection driver comprising an LPI fuel pump and an LPI injector; and a controller for controlling the gasoline driver and the LPI driver, and increasing and reducing ratios of fuels injected into the engine upon a fuel switch request while simultaneously injecting the fuels, characterized in that the controller comprises: a calculation unit for calculating an injection amount of a replacing fuel if the fuel switch request is input, and calculating based on the calculated injection amount an injection ratio and an injection time of the replacing fuel, and an injection ratio and an injection time of a previous fuel; a determination unit for determining whether to solely inject the previous fuel based on the injection time of the replacing fuel calculated by the calculation unit, and determining whether to solely inject the replacing fuel based on the injection time of the previous fuel calculated by the calculation unit; and a control unit for controlling the calculation unit to calculate the injection ratio and the injection time of the previous fuel if the determination unit determines not to solely inject the previous fuel, and controlling the gasoline driver and the LPI driver to inject fuels at corresponding injection ratios calculated by the calculation unit if the determination unit determines not to solely inject the replacing fuel. an engine using gasoline and LPG as fuels; a gasoline driver comprising a gasoline fuel pump and a gasoline injector; a liquefied petroleum injection driver comprising an LPI fuel pump and an LPI injector; and a controller for controlling the gasoline driver and the LPI driver, and increasing and reducing ratios of fuels injected into the engine upon a fuel switch request while simultaneously injecting the fuels, characterized in that the controller comprises: a calculation unit for calculating an injection amount of a replacing fuel if the fuel switch request is input, and calculating based on the calculated injection amount an injection ratio and an injection time of the replacing fuel, and an injection ratio and an injection time of a previous fuel; a determination unit for determining whether to solely inject the previous fuel based on the injection time of the replacing fuel calculated by the calculation unit, and determining whether to solely inject the replacing fuel based on the injection time of the previous fuel calculated by the calculation unit; and a control unit for controlling the calculation unit to calculate the injection ratio and the injection time of the previous fuel if the determination unit determines not to solely inject the previous fuel, and controlling the gasoline driver and the LPI driver to inject fuels at corresponding injection ratios calculated by the calculation unit if the determination unit determines not to solely inject the replacing fuel. a calculation unit for calculating an injection amount of a replacing fuel if the fuel switch request is input, and calculating based on the calculated injection amount an injection ratio and an injection time of the replacing fuel, and an injection ratio and an injection time of a previous fuel; a determination unit for determining whether to solely inject the previous fuel based on the injection time of the replacing fuel calculated by the calculation unit, and determining whether to solely inject the replacing fuel based on the injection time of the previous fuel calculated by the calculation unit; and a control unit for controlling the calculation unit to calculate the injection ratio and the injection time of the previous fuel if the determination unit determines not to solely inject the previous fuel, and controlling the gasoline driver and the LPI driver to inject fuels at corresponding injection ratios calculated by the calculation unit if the determination unit determines not to solely inject the replacing fuel.