Abstract: A new kind of real-time power control system of fast flow CO2 lasers is developed to improve the stability of laser power,which is composed of two parts:sampling unit and feedback control unit.In the sampling unit,an infrared detector is used to sample the laser power output from the rear mirror of the resonator.With an attenuator inserted between the detector and the rear mirror to prevent the detector from damage by the laser.In the feedback control system,the sampling signal is compared with the setting reference value,and the discharge current is automatically adjusted to make the output laser power stable around the setting power.The experimental results indicate that this system can automatically control the laser power on line,and greatly enhance the stability and accuracy of the laser power without any accessory inserted in the output laser path.This system has been successfully used in a 4kW fast-flow CO2 laser with much better output power stability of ±0.1%.