Abstract: The calibration repeatability of CO₂ laser and the power range that can be calibrated are reduced by the laser's poor power stability and adjustability. The repeatability can be improved by monitoring the CO₂ laser power in real time with a beam splitting system. But for 10.6 μm laser, the reflectance of ZnSe beam splitters is very unstable, which leads to fluctuation of the monitor ratio. Based on the principle of chopper, a chopper sampling and attenuation system was developed. The attenuation range is 0.2%~50%. Through an optimization design of the control unit, the interference between two sets of choppers in the same beam was avoided. The monitor ratio of the calibration setup was tested, and the monitor ratio instability was less than 1.1%, which is significantly better than that of ZnSe beam splitters (8.6%). The repeatability (k = 1) of the correction factor of the measured laser power meter improved from 1.09% (without a monitor) to 0.62%. The chopper sampling and attenuation system proposed in this paper improves the repeatability of calibration results and increases the power adjustment capability in CO₂ laser power calibrations.