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.