Abstract: A series standard of CAI of conodonts is established through heat tests and colour observations in the field. From determination of Ro% and colour observation of conodonts of a same rock sample, the relationship between CAI value and Ro% of vitrites is derived,which indicates that the CAI value may be used as one of the indices of maturity of organic matter.It has been identified that the colour of conodonts distributed in the Permian aud Triassic rocks in Hubei varies from place to place. The organic matter in the Permian and Triassic in Tianmen, Chenhu, Sangzhi, Xingshan etc., rauges from matured to highly-matured, giving a better oil and gas prospect; while those in Lichuan, Jiannan and eastern Sichuan are over-matured and good for gas generation only.