Liquid-solid two-phase flow widely exists in industrial process and the online measurement of particle size distribution is important to the production optimization and control. As an undisturbed multiphase flow parameter measurement method, ultrasonic method's attenuation characteristics are closely related to the particle size and volume fraction of solid particles, and can be used to measure the particle size distribution online. Experimental devices for ultrasonic attenuation of liquid-solid two-phase medium were established. In the experiments silica sand is used as the solid particles and tap water is used as liquid phase. Chirp ultrasonic signal is used to excite and study the ultrasound attenuation characteristics of the liquid-solid two-phase medium. The experiment results show that with the increasing of the excitation frequency and solid volume fraction, the ultrasonic attenuation coefficient rises gradually. Twomey algorithm and genetic algorithm are used to inverse the particle size distribution of liquid-solid two-phase medium, the measurement results are compared with those of Malvern laser particle size analyzer, and the correlation coefficient is 0. 918.