Based on a cold model experiment setup of a coupled reactor mainly composed of lower riser and upper fluidized bed, an experiment was measured and analyzed the pressure fluctuation in the riser under the work mode of operating bed existing and not existing. Experimental result and analysis show that the standard deviation of pressure fluctuation in the riser is obviously higher when the operating bed exist. The frequency of pressure fluctuation mainly around 1.56?3.13 and 0?0.391 Hz when the operating bed not exist, and around 12.5?25.0 and 0?0.391 Hz when the operating bed exist. The 1.56?3.13 Hz mainly result from the fluctuation of particles in the riser, while the 12.5?25.0 Hz result from the gas?solid distributor locating at the exit of the riser, the restriction of gas?solid flow caused by upper fluidized bed and the gas fluctuation this restriction resulting in. The 0?0.391 Hz mainly result from the discontinuous feedstock of riser and the interaction it caused with the underneath lifting gas.