Abstract: In this paper,formation and evolution of bicyclic sesquiterpane in wooden coal from Nanning Basin are studied by means of pyrolysis. Besides of the peralent method which heats a certain number of raw samples at different temperature, a new one which heats only one sample step by step from the low to the high temperature was used. The fist series experiment is called Y series and the second one is called Z series. The Y series represented the thermal evolution of comprehensive primary organic matter,and the Z sereis represented the pyrolysis of kerogen,the two series of constracting experiments had born much information. On the m/z 123 mass chromatogram seven bicyclic sesquiterpane compounds are determined.Peak 1,2,3 are pentamethyl一naphthalene,drimane and pentamethyl一naphthalene respectively which molecules are C₁₅H₂₈, and Peak 4,5,6,7 are ethyl,tetramethyl一naphthalene,ethyl, tetramethyl一naphthalene,homodrimane and ethyl,tetramethyl一naphthalene which molecules are C₁₆H₃₀ There were many differences between Y and Z sereis experiments. 1n Y series, the seven compounds were all present at the temperature below 300℃, compound No. 2,3,6,7 were present at 350℃,the one No. 2,6,7 were present at 400℃ and no this kind of compounds appeared at the temperature higher than 4000C.Peak 6 was the main in the raw sample, peak 7 was the main in the range of 250一300℃ and peak 6 was the main in range of 350一400'C .Peak 1,4,5 reduced throughout in the whole process and disappeared at 350℃.Peak 7 riled at the temperature below 300℃ and reduced then. In pace whith the temperaure rising, the others reduced at fist and riled then,Peak 3 maintained about the same at the temperature below 300℃ and reduced at 3500C and disappeared at 400℃.In Z series, the bicyclic sesquiterpanes were mainly compound 2,6,7.Compound No. 7 was the main one in the range of 250一300℃ and No. 6 is the main at 350℃.1n pace whith the temperature rising, peak 2,6 became higher and peak 7 reduced. No bicyclic sesquiterpanes were present at 400'C.On the basis of above analysis, two ways of bicyclic sesquiterpanes were defined. Compound No. 1,3,4,5 and a little of one No. 2,6,7 were generated probably from organic matzer of non一kerogen,and the ones No. 2,6,7 were formed mainly from kerogen. It is considered generally that drimane/homodrimane ratio increases gradually with thermal evolution,so it is can be used as a maturation index.But the experiment showed that the ratio decreased gradually till 300℃ and then increased at the higher temperature,so it is not a good maturation index,the other maturation parameters are not either. Only the drimane/pentamethyl一naphthalene(compound No. 1)ratio increased linearly along with temperature rising, and it can be used as a good maturation index.