A hydraulic control valve system for a construction machine, comprising: a hydraulic pump connected to an engine; a swing spool installed on an upstream side of a center bypass path that fluidically communicates with a discharge flow path of the hydraulic pump and configured to be shifted to control a start, a stop, and a direction change of a swing motor; an arm spool installed on a downstream side of the center bypass path and configured to be shifted to control a start, a stop, and a direction change of an arm cylinder; and characterized in that the hydraulic control valve further comprising a center bypass control valve installed within the arm spool, the center bypass control valve being configured to be shifted by a pressure of a hydraulic fluid discharged from the hydraulic pump, which is increased during a combined operation in which a swing manipulation and an arm manipulation are simultaneously performed, and configured to unload an increased pressure on a swing side to the center bypass path during the shift thereof characterised in that the center bypass control valve comprises: a sleeve installed within the arm spool and having a flow path formed therein so as to fluidically communicate with the discharge flow path of the hydraulic pump; a first piston slidably installed within the sleeve and configured to be shifted to maintain the arm side load pressure through unloading of a part of the discharged hydraulic fluid on the hydraulic pump side to the center bypass path during the combined operation in which the swing manipulation and the arm manipulation are simultaneously performed;a second piston configured to be in close contact with one end of the first piston and to be shifted to press the first piston by the load pressure which is variably increased depending on a swing side pilot pressure that is additionally applied to the arm side load pressure during the combined operation in which the swing manipulation and the arm manipulation are simultaneously performed; and a third piston elastically installed on the other end of the first piston by a valve spring. a hydraulic pump connected to an engine; a swing spool installed on an upstream side of a center bypass path that fluidically communicates with a discharge flow path of the hydraulic pump and configured to be shifted to control a start, a stop, and a direction change of a swing motor; an arm spool installed on a downstream side of the center bypass path and configured to be shifted to control a start, a stop, and a direction change of an arm cylinder; and characterized in that the hydraulic control valve further comprising a center bypass control valve installed within the arm spool, the center bypass control valve being configured to be shifted by a pressure of a hydraulic fluid discharged from the hydraulic pump, which is increased during a combined operation in which a swing manipulation and an arm manipulation are simultaneously performed, and configured to unload an increased pressure on a swing side to the center bypass path during the shift thereof characterised in that the center bypass control valve comprises: a sleeve installed within the arm spool and having a flow path formed therein so as to fluidically communicate with the discharge flow path of the hydraulic pump; a first piston slidably installed within the sleeve and configured to be shifted to maintain the arm side load pressure through unloading of a part of the discharged hydraulic fluid on the hydraulic pump side to the center bypass path during the combined operation in which the swing manipulation and the arm manipulation are simultaneously performed;a second piston configured to be in close contact with one end of the first piston and to be shifted to press the first piston by the load pressure which is variably increased depending on a swing side pilot pressure that is additionally applied to the arm side load pressure during the combined operation in which the swing manipulation and the arm manipulation are simultaneously performed; and a third piston elastically installed on the other end of the first piston by a valve spring.