Abstract: For large optics of high-power laser facility, the controlling technology of mid-spatial frequency error is developed. Firstly, the CCOS convolution residual error caused by regular path is analyzed, and the residual error model is established. And then, the optimization parameters for controlling mid-spatial frequency error are achieved by this model. Finally, according to the optimization parameters, the mid-spatial frequency error of 400 mm aperture window is remarkably improved. After several CCOS iteration, the peak-to-valley(PV) is 170.856 nm, the root-mean-square(RMS) of PSD1 is 1.67 nm and no obvious mid-spatial frequency error is found. The result shows that the mid-spatial frequency error of 400 mm aperture window is under control, and the 400 mm aperture windows can be achieved and meet the requirement of mid-spatial frequency error in high-power laser facility.