A method of controlling a flow rate of a construction machine, the method comprising: detecting (S210) a rotation position of at least one of working devices including a boom (B), an arm (A) and an attachment (T) of the construction machine; determining (S220) whether the detected working device reaches to a maximum position (A1, A2, B1, B2, T1, T2) or not, wherein the boom (B) is rotatable from a maximum descent position (B1) to a maximum ascent position (B2), which positions correspond to a maximum position of the boom (B), wherein the arm (A) is rotatable from a maximum descent position (A1) to a maximum ascent position (A2), which positions correspond to a maximum position of the arm (A), and wherein the attachment (T) is rotatable from a maximum descent position (T1) to a maximum ascent position (T2), which positions correspond to a maximum position of the attachment (T); cutting off (S230) 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 (S240) whether a fuel reduction mode is selected or not; reducing (S250), 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 (S260) whether a capacity improvement mode is selected or not when the fuel reduction mode is not selected; and supplying (S270), 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 (S210) a rotation position of at least one of working devices including a boom (B), an arm (A) and an attachment (T) of the construction machine; determining (S220) whether the detected working device reaches to a maximum position (A1, A2, B1, B2, T1, T2) or not, wherein the arm (A) is rotatable from a maximum descent position (A1) to a maximum ascent position (A2), which positions correspond to a maximum position of the arm (A), and wherein the attachment (T) is rotatable from a maximum descent position (T1) to a maximum ascent position (T2), which positions correspond to a maximum position of the attachment (T); cutting off (S230) 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 (S240) whether a fuel reduction mode is selected or not; reducing (S250), 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 (S260) whether a capacity improvement mode is selected or not when the fuel reduction mode is not selected; and supplying (S270), 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 (S230) 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 (S240) whether a fuel reduction mode is selected or not; reducing (S250), 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 (S260) whether a capacity improvement mode is selected or not when the fuel reduction mode is not selected; and supplying (S270), 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. <EOS>