The invention relates to an 
ultrasonic attenuation spectrum principle based method for measuring the average particle size and concentration of two types of mixed 
solid particles in a liquid or gas medium. The 
ultrasonic attenuation spectrum principle based method comprises the following steps of step 1, measuring an experimental measurement 
ultrasonic attenuation spectrum alpha (f) under the condition that the two types of 
solid particles A and B are located in a measurement area, wherein f is the ultrasonic frequency; step 2, calculating an 
acoustic attenuation coefficient Kext of the particle and 
acoustic wave effect; step 3, determining whether the particles are A particles or B particles and determining whether phonons are absorbed or scattered through the 
acoustic attenuation coefficient; step 4, calculating a scattering emergence angle theta M1 of the scattered phonons; step 5, continuing to calculate a theoretical ultrasonic attenuation spectrum through a result of the step 4; step 6, establishing an objective function according to the theoretical ultrasonic attenuation spectrum and the experimental measurement ultrasonic attenuation spectrum to solve the particle size and 
volume concentration. The ultrasonic attenuation spectrum based mixed 
solid particle size and concentration measurement method can be applied to the two types of mixed solid particles and laboratory scientific research and the online measurement and the application of the industrial field can be implemented.