A system for filling an LPG vehicle with LPG using an auxiliary bombe is provided. The system may be configured for easily filling a main bombe with LPG even in the hot season (summertime) or the like during which the outside temperature rapidly rises, by using an auxiliary bombe in addition to using the main bombe. The system may also be capable of always smoothly refilling the main bombe with LPG by moving a portion of the LPG in the main bombe to the auxiliary bombe, when the pressure in the main bombe is higher than the LPG filling pressure of a filling gun in the hot season during which the outside temperature rapidly rises, so that the pressure in the main bombe becomes lower than the filling pressure.