A control system for construction machinery, comprising: a main control valve installed in a hydraulic line between a hydraulic pump and actuators (10a, 10b, 10c, 20a, 20b, 20c), and including a first spool (310a, 310b and 310c) and a second spool (320a, 320b, 320c), a first group of electro proportional pressure reducing valves outputting a secondary pressure in proportion to a pressure command signal to the first spool (310a, 310b and 310c) for controlling a first group of actuators (10a, 10b, 10c) of the actuators (10a, 10b, 10c, 20a, 20b, 20c), and a second group of electro proportional pressure reducing valves outputting a secondary pressure in proportion to a pressure command signal to the second spool (320a, 320b, 320c) for controlling a second group of actuators (20a, 20b, 20c) of the actuators (10a, 10b, 10c, 20a, 20b, 20c); a first control valve installed in a first control line through which a pilot working fluid is supplied to the first group of electro proportional pressure reducing valves and configured to selectively open and close the first control line; a second control valve installed in a second control line through which a pilot working fluid is supplied to the second group of electro proportional pressure reducing valves and configured to selectively open and close the second control line; characterized in that the control system further comprises a first pressure sensor configured to detect the secondary pressure outputted from the first group of electro proportional pressure reducing valves and a second pressure sensor configured to detect the secondary pressure outputted from the second group of electro proportional pressure reducing valves; and a controller configured to output the pressure command signals to the electro proportional pressure reducing valves (312, 322) corresponding to a manipulation signal of the construction machinery, and configured to compare the secondary pressures detected by the first and second pressure sensors (314, 324) and the pressure command signals to determine whether or not the electro proportional pressure reducing valves (312, 322) fail; wherein when it is determined that any one of the first group of electro proportional pressure reducing valves fails, the controller closes the first control valve to block the pilot working fluid from being supplied to the first group of electro proportional pressure reducing valves, and when it is determined that any one of the second group of electro proportional pressure reducing valves fails, the controller closes the second control valve to block the pilot working fluid from being supplied to the second group of electro proportional pressure reducing valves. a main control valve installed in a hydraulic line between a hydraulic pump and actuators (10a, 10b, 10c, 20a, 20b, 20c), and including a first spool (310a, 310b and 310c) and a second spool (320a, 320b, 320c), a first group of electro proportional pressure reducing valves outputting a secondary pressure in proportion to a pressure command signal to the first spool (310a, 310b and 310c) for controlling a first group of actuators (10a, 10b, 10c) of the actuators (10a, 10b, 10c, 20a, 20b, 20c), and a second group of electro proportional pressure reducing valves outputting a secondary pressure in proportion to a pressure command signal to the second spool (320a, 320b, 320c) for controlling a second group of actuators (20a, 20b, 20c) of the actuators (10a, 10b, 10c, 20a, 20b, 20c); a first control valve installed in a first control line through which a pilot working fluid is supplied to the first group of electro proportional pressure reducing valves and configured to selectively open and close the first control line; a second control valve installed in a second control line through which a pilot working fluid is supplied to the second group of electro proportional pressure reducing valves and configured to selectively open and close the second control line; characterized in that the control system further comprises a first pressure sensor configured to detect the secondary pressure outputted from the first group of electro proportional pressure reducing valves and a second pressure sensor configured to detect the secondary pressure outputted from the second group of electro proportional pressure reducing valves; and a controller configured to output the pressure command signals to the electro proportional pressure reducing valves (312, 322) corresponding to a manipulation signal of the construction machinery, and configured to compare the secondary pressures detected by the first and second pressure sensors (314, 324) and the pressure command signals to determine whether or not the electro proportional pressure reducing valves (312, 322) fail; wherein when it is determined that any one of the first group of electro proportional pressure reducing valves fails, the controller closes the first control valve to block the pilot working fluid from being supplied to the first group of electro proportional pressure reducing valves, and when it is determined that any one of the second group of electro proportional pressure reducing valves fails, the controller closes the second control valve to block the pilot working fluid from being supplied to the second group of electro proportional pressure reducing valves.