Cirrus optical thickness is one of the cloud optical parameters that have great influence on global climate and earth radiation budget. In military, atmospheric science and other fields, there is a wide demand for cirrus optical parameter solving algorithm. Moderate-resolution imaging spectroradiometer (MODIS) data is used to solve cirrus parameters, and satellite multi-channel data is mostly used, so the data processing process is relatively complex. The RT3 model combined with MODIS cloud parameters was proposed to simulate and calculate cirrus reflectance, and a cirrus optical thickness lookup table was established. A simple algorithm was designed to achieve effective inversion of cirrus optical thickness. The correlation coefficient between the inversion results of cirrus optical thickness and the actual data measured by MODIS is 0.97, which verifies the reliability of cirrus optical thickness inversion. By selecting MODIS data at different time periods, the variation of cirrus optical thickness in different time and space ranges is analyzed, and the average error is less than 0.16, which further verifies the effectiveness of the RT3 model-based lookup table for inversion of cirrus optical thickness. The results are helpful to realize simple and effective inversion of cirrus optical properties worldwide.