A new technique combining Py-GC/MS with TG/MS can be used in analyzing the mechanism and kinetic modelling of pyrolysis. The results of this study show that a combined approach of Py-GC/MS and TC/MS exhibited dynamic curves of 13 evolved gases from the pyrolysis of PEEK from room temperature to 900 degrees C. In this study we also discovered that there are two stable pyrolysis reaction regions during the pyrolysis in helium atmosphere at a heating rate of 10 degrees C/min from room temperature to 900 degrees C. In the first pyrolysis region the ether group and ketone group from the main chain of PEEK decomposed to phenol and CO2, respectively. It also showed that the thermal stability of the ketone group was better than that of the ether group. Accompanied with the chain transfer in the first pyrolysis region, the fluorenone structure appeared in part of the carbonization scheme. Above 650 degrees C it moved to the second reaction region. In this region the main decomposition products were CO2 from the ketone group of fluorenone and from the carbonized structure described above. From the two flat regions of the activation energy curve of pyrolysis, we have proposed a kinetic model with two pyrolysis regions. Based on this model, we compared the theoretical pyrolysis curve with the experimental curve, the two curves being quite similar.