A system for automatically exchanging a battery of an electric vehicle, including a horizontal frame of a predetermined area formed at a location higher than the electric vehicle; a plurality of battery stands formed on a bottom surface of the horizontal frame at a predetermined interval; a pair of fixed guide rails arranged and installed on front and rear sides or left and right sides of the horizontal frame, respectively; a variable guide rail adapted to move horizontally along X-axis or Y-axis along the fixed guide rails; a movable rail adapted to move horizontally along Y-axis or X-axis along the variable guide rail and ascend/descend vertically; and a grasping part installed on a lower end of the movable rail and adapted to pick up a battery of the electric vehicle or a battery seated on the battery stand and exchange each other.