The free radicals in kerogen of sedimentary organic matter can be easily d etermined by using the electron paramagnetic resonance(EPR) technique. The spin density(Ng) is a valid thermal index of organic matter evolution. A history of heat flow variation of a Cenozoic basin was inversed by using modelling compu tation of Ng values obtained from the kerogen samples of maturity series. The he at flow increases with the evolution of basin, which also can be proved by using the vitrinite reflectance (Ro) inverse method.