A control system for a hydraulic construction machine comprising: a prime mover; at least one variable displacement hydraulic pump (1, 2) driven by said prime mover; at least one hydraulic actuator driven by a hydraulic fluid from said hydraulic pump; revolution speed control means for controlling a revolution speed of said prime mover; pump absorption torque control means for reducing a maximum displacement of said hydraulic pump with a rise of the load pressure of said hydraulic pump (1, 2) when a load pressure of said hydraulic pump becomes higher than a fourth value, such that maximum absorption torque of said hydraulic pump does not exceed a setting value; and mode selection means for selecting a control mode related to said prime mover; load pressure detection means (75, 76) for detecting load pressure of said hydraulic pump (1, 2); and target revolution speed setting means (70, 700a-700g) which stores a prime mover revolution speed preset therein to reduce the revolution speed of said prime mover with a rise of the load pressure of said hydraulic pump (1, 2), and which, when a particular mode is selected by said mode selection means, determines a corresponding prime mover revolution speed (ΔN0) by referring to the preset prime mover revolution speed based on the load pressure of the hydraulic pump (1, 2) detected by said load pressure detection means (75, 76) and sets a target revolution speed for said revolution speed control means based on the determined prime mover revolution speed, wherein said target revolution speed setting means (70, 700a-700g) sets, as the target revolution speed, a rated target revolution speed (Nmax) of said prime mover when the load pressure detected by said load pressure detection means (75, 76) is not higher that a preset value, and reduces the target revolution speed with a rise of the load pressure when the load pressure detected by said load pressure detection means exceeds the preset value, wherein the preset value is set close to said fourth value. a prime mover; at least one variable displacement hydraulic pump (1, 2) driven by said prime mover; at least one hydraulic actuator driven by a hydraulic fluid from said hydraulic pump; revolution speed control means for controlling a revolution speed of said prime mover; pump absorption torque control means for reducing a maximum displacement of said hydraulic pump with a rise of the load pressure of said hydraulic pump (1, 2) when a load pressure of said hydraulic pump becomes higher than a fourth value, such that maximum absorption torque of said hydraulic pump does not exceed a setting value; and mode selection means for selecting a control mode related to said prime mover; load pressure detection means (75, 76) for detecting load pressure of said hydraulic pump (1, 2); and target revolution speed setting means (70, 700a-700g) which stores a prime mover revolution speed preset therein to reduce the revolution speed of said prime mover with a rise of the load pressure of said hydraulic pump (1, 2), and which, when a particular mode is selected by said mode selection means, determines a corresponding prime mover revolution speed (ΔN0) by referring to the preset prime mover revolution speed based on the load pressure of the hydraulic pump (1, 2) detected by said load pressure detection means (75, 76) and sets a target revolution speed for said revolution speed control means based on the determined prime mover revolution speed, wherein said target revolution speed setting means (70, 700a-700g) sets, as the target revolution speed, a rated target revolution speed (Nmax) of said prime mover when the load pressure detected by said load pressure detection means (75, 76) is not higher that a preset value, and reduces the target revolution speed with a rise of the load pressure when the load pressure detected by said load pressure detection means exceeds the preset value, wherein the preset value is set close to said fourth value.