Previously, ozone products could not be generated due to the abnormal solar irradiance for a total ozone unit (TOU) on FY-3C, because the instrumental degradation coefficient could not be measured. After investigating the irradiation measurement data and degradation trends of FY-3B/TOU and combining this with FY-3C/TOU radiance and irradiance data, methods for calculating instrumental degradation coefficients were explored based on clear ocean pixel data. An area in the atmosphere above the Pacific Ocean was chosen as a representative “clean” atmospheric sample, which is an area without pollution, to calculate the radiation from the earth and the model radiation with a vector radiative transfer mode. By selecting clear pixels and comparing measured and modeled values, the FY-3C/TOU instrument degradation with time was evaluated. On comparing the new total ozone results with WMO/WOUDC data, it is found that the change in the satellite monitoring data over time and the site results agreed well. Further, the mean square error of the two results is within 5%. Thus, the clear-sky pixels method for FY-3C/TOU works well and has the potential to solve problems regarding in-orbit radiation calibrations.