Abstract: Six kinds of PAN samples are studied by DTA,TG,TPDR,determination of functional groups containing oxygen and analysis of pore texture. The results show that the difference of sample composition leads to the difference of carboxy number,and the increase of carboxy number leads to the decrease of special area. Heat effects of cycligation reaction for six samples are different and the pure polymer generates more heat than other samples. The heat generated by the reaction is decreased after the introduction of carboxy group. With increasing of carbory number of samples bulk or decreasing of special area,activation energy of cycligation reaction is decreased.When cycligation reaction for PAN happened in air,the various steps happen in following order; oxidation,cycligation of cyan-thermal decomposition and dehydrogenatien.