A method of controlling a flow rate of a construction machine, the method comprising: detecting a rotation position of at least one of working devices including a boom, an arm and an attachment of the construction machine; determining whether the detected working device reaches to a maximum position (A1, A2, B1, B2, T1, T2) or not, wherein the boom is rotatable from a maximum descent position to a maximum ascent position, which positions correspond to a maximum position of the boom, wherein the arm is rotatable from a maximum descent position to a maximum ascent position, which positions correspond to a maximum position of the arm, and wherein the attachment is rotatable from a maximum descent position to a maximum ascent position, which positions correspond to a maximum position of the attachment; cutting off a flow rate supplied to the detected working device when the detected working device reaches the maximum position (A1, A2, B1, B2, T1, T2), characterised by identifying whether a fuel reduction mode is selected or not; reducing, by a main controller, a discharge amount of a pump corresponding to a cut-off flow rate when the fuel reduction mode is selected; identifying whether a capacity improvement mode is selected or not when the fuel reduction mode is not selected; and supplying, by the main controller, a cut-off flow rate to at least one of the working devices that do not reach to the maximum position. detecting a rotation position of at least one of working devices including a boom, an arm and an attachment of the construction machine; determining whether the detected working device reaches to a maximum position (A1, A2, B1, B2, T1, T2) or not, wherein the arm is rotatable from a maximum descent position to a maximum ascent position, which positions correspond to a maximum position of the arm, and wherein the attachment is rotatable from a maximum descent position to a maximum ascent position, which positions correspond to a maximum position of the attachment; cutting off a flow rate supplied to the detected working device when the detected working device reaches the maximum position (A1, A2, B1, B2, T1, T2), characterised by identifying whether a fuel reduction mode is selected or not; reducing, by a main controller, a discharge amount of a pump corresponding to a cut-off flow rate when the fuel reduction mode is selected; identifying whether a capacity improvement mode is selected or not when the fuel reduction mode is not selected; and supplying, by the main controller, a cut-off flow rate to at least one of the working devices that do not reach to the maximum position. cutting off a flow rate supplied to the detected working device when the detected working device reaches the maximum position (A1, A2, B1, B2, T1, T2), characterised by identifying whether a fuel reduction mode is selected or not; reducing, by a main controller, a discharge amount of a pump corresponding to a cut-off flow rate when the fuel reduction mode is selected; identifying whether a capacity improvement mode is selected or not when the fuel reduction mode is not selected; and supplying, by the main controller, a cut-off flow rate to at least one of the working devices that do not reach to the maximum position.