The relations of the maximum paleo-geotemperature and vitrinite reflectance with Kübler index (K.I.) of illite crystallinity were characterized, based on the analysis of the K.I. determined by X-ray diffraction (XRD), the maximum paleo-geotemperature reconstructed by apatite fission track (AFT) and vitrinite reflectance (Ro) data. The logarithmic relationship between the maximum paleo-geotemperature and K.I. was revealed: T=-148.95×ln (K.I.) +86.77 (℃); Ro=-3.069×ln (K.I.) +0.068 (%). This relationship has a temperature range of 130~300°C for wide using in geological process, and can be considered as a simple function to convert K.I. to paleo-geotemperature and Ro. This method provides a way for the selection of the thermal history geologic thermometer combination of marine-continental superimposed basin. Comparing to Ro and AFT, the illite crystallinity index is still controversial to be generally used as a maturity and geothermal indicator for the thermal history reconstruction of sedimentary rocks due to the lack of an effective thermal evolution model.