The methods to reconstruct thermal history of basins are divided into two types,paleotemperature scales and thermal dynamics of basin.The most popular paleotemperature indices include maturity of organic matter and fission track of minerals.The thermal dynamics models of basins include lithosphere stretch model and compressional model.This paper studies the free radicals concentrated in type I organic matter as a thermal indicator in sedimentary basins.The thermal evolution characteristic of the free radical in type I organic matter of the samples was analyzed.Based on free radical concentration(Ng) and time-temperature index(TTI) data of the geological type I organic matter samples,the data of the thermal simulation type I organic matter samples are corrected.Then the quantitative model between free radical concentration(Ng) of organic matter and time-temperature index(TTI) for type I organic matter was obtained according to the data of the corrected thermal simulation samples.