Abstract： The low-fusion-temperature polyethylene particles were used to simulate the process of high-temperature defluidization in a two-dimensional semithermal circulating fluidized bed. The process of defluidization can be divided into five stages, including fusion, layering, nucleation, agglomeration and shutdown. The time-domain analysis shows that pressure changes can reflect the approximate time of the occurrence of defluidization and the changes of standard deviation preceding the changes of average value. The frequencydomain analysis shows that the changes of dominant frequency in spectrogram are more obvious than that of average value, which makes it possible to prevent defluidization. By comparing the spectrogram of different measuring points, the earliest position of the defluidization can be obtained.