A control system for a hybrid excavator including an engine, a hydraulic pump driven by the engine to drive a hydraulic actuator by hydraulic fluid discharged therefrom, an electric generator driven by the engine to generate electric energy, and an electric energy storage device for charging the electric energy generated by the electric generator and supplying the electric energy to an electric actuator, the control system comprising: a required torque detection means for detecting a torque that is required to drive the hydraulic pump; a charge amount detection means for detecting a charge rate (or charge amount) of the electric energy storage device; a memory for storing a degree of electricity generation (or amount of electricity generation) based on the torque and the charge rate (or charge amount); a hybrid control means for controlling the electric generator based on the amount of electricity generation stored in the memory, which corresponds to both the torque value detected by the required torque detection means and the charge rate (or charge amount) value detected by the charge amount detection means; a charging means for charging the electric energy storage device by operating the engine in an appropriate torque region of a different revolution that is suitable for electricity generation if the required torque detection means detects a torque that is lower than a predetermined level, which is determined to correspond a standby state in which no work is done; an engine revolution adjustment unit for reducing the engine revolution to a low RPM with small fuel consumption if the required torque detection means detects a torque that is lower than a predetermined level, which is determined to correspond to a standby state in which no work is done; and an electric generator driving unit for driving the electric generator at a level that is higher than a predetermined level if the required torque detection means detects a torque that is lower than a predetermined level, which is determined to correspond to a standby state in which no work is done. a required torque detection means for detecting a torque that is required to drive the hydraulic pump; a charge amount detection means for detecting a charge rate (or charge amount) of the electric energy storage device; a memory for storing a degree of electricity generation (or amount of electricity generation) based on the torque and the charge rate (or charge amount); a hybrid control means for controlling the electric generator based on the amount of electricity generation stored in the memory, which corresponds to both the torque value detected by the required torque detection means and the charge rate (or charge amount) value detected by the charge amount detection means; a charging means for charging the electric energy storage device by operating the engine in an appropriate torque region of a different revolution that is suitable for electricity generation if the required torque detection means detects a torque that is lower than a predetermined level, which is determined to correspond a standby state in which no work is done; an engine revolution adjustment unit for reducing the engine revolution to a low RPM with small fuel consumption if the required torque detection means detects a torque that is lower than a predetermined level, which is determined to correspond to a standby state in which no work is done; and an electric generator driving unit for driving the electric generator at a level that is higher than a predetermined level if the required torque detection means detects a torque that is lower than a predetermined level, which is determined to correspond to a standby state in which no work is done.