In this study, we discuss the O₂-O₂ inversion effective cloud fraction of the absorption band observed at 477 nm. First, the O₂-O₂ slant column densities are retrieved in 460--490 nm using the differential optical absorption spectroscopy (DOAS) algorithm, and the stripes occurring in the O₂-O₂ slant column densities are corrected. Second, the SCIATRAN radiative transfer model is used to set different nodes with respect to solar zenith angle, viewing zenith angle, relative azimuth angle, surface albedo, surface altitude, cloud fraction, and cloud pressure to establish the lookup table of the O₂-O₂ slant column densities and reflectance. Subsequently, we invert the aforementioned lookup table to obtain the lookup table of cloud fraction. Finally, we use the O₂-O₂ slant column densities, continuum reflectance, and related solar geometry information to perform multi-dimensional interpolation for obtaining the effective cloud fraction for the environmental trace gas monitoring instrument (EMI). The EMI results are compared with the OMI (ozone monitoring instrument) cloud fraction to verify the accuracy of the proposed algorithm and both denote that the frequency percentages decrease from low cloud cover to high cloud cover. When the cloud fractions are 0 and 1, their frequency percentages are observed to be considerably high. The OMI and EMI cloud fractions are in good agreement and have a high correlation coefficient (R) of 0.82.