The invention discloses a sound wave detection method for a fluidized state of a viscous particle fluidized bed reactor. A viscous particle fluidized bed is detected by using a sound emission signal detection method; and a fluidization behavior is characterized by receiving a sound signal generated by collision among particles and impact of the particles on the wall surface in a fluidization process. In addition, the material level is the position, farthest away from a distribution plate, of the top of a sound wave energy peak; the sound wave energy above the material level is rapidly reduced;based on this, the bed height of the fluidized bed is judged; and a bed expansion ratio and bed voidage can be obtained in combination with the static bed height of the fluidized bed during initial packing. When a plurality of energy peak values occur in a certain position, it is considered that the viscous particle fluidized bed has a sound wave energy peak value in the middle of the bed, wherein the last peak position of the sound wave energy represents the bed height; and then the bed expansion ratio and the bed voidage can be obtained in combination with the static bed height of the fluidized bed static bed. According to the method, the wall of the reactor does not need to be invaded in a detection process, so that the problem of fine powder blockage can be fundamentally avoided; andthe method can be used for detecting the axial fluidized state distribution of the viscous particle fluidized bed.