Abstract: Because of the wide cross section,the large-scale circulating fluidized bed (CFB) boilers with one combus- tion chamber and one distributer were sometimes operated accompanying with severe lateral bed pressure fluctuations, which posed a serious threat to the stability and safety of the boilers. In order to interpret the mechanisms of lateral bed pressure fluctuations in large-scale CFB boilers in theory,a nonlinear long standing wave model for a shallow bed of bed pressure fluctuations and mathematical models of the fluidization in dense-phase were built. The structure sizes, operational parameters and bed pressure measured data of two 300 MW subcritical CFB boilers were used to determine the model parameters. The coupling calculation results of models show that the simulation results of the amplitudes and periods of pressure fluctuations are presented in good agreement with the corresponding measured data. Bed pressure distribution along the bed width,the amplitudes and periods of lateral bed pressure fluctuations,the heights of the ac- tive section and inactive section,and voidage distribution in inactive section,all have a certain relationship with the static bed height.