Abstract: A method for determining spherical polypropylene catalyst strength by ultrasonication with a laser particle size analyzer is founded. The effect of ultrasonic power, stirring speed, concentration of the solution, the depth of the ultrasonic probe inserted into the solution on catalyst crush was investigated. Moreover，the strength of spherical polypropylene catalyst and their carrier were also measured for comparison. The tests indicate that for GS13L ultrasonic probe, the power tested within the specified range has no effect on the degree of fragmentation. No crushing of the sample was observed without stirring during ultrasonic process. The degree of fragmentation is higher at 200 r.min-1 speed of stirring than that of 400 r.min-1 stirring speed. It is found that the degree of fragmentation decreases with increase of the concentration of the solution. When the depth of the ultrasonic probe inserted into the solution is larger than 20mm, the efficiency of fragmentation will decline. In addition, it shows that the greater the strength of the carrier is, the greater the strength of the catalyst is. The strength of spherical polypropylene catalyst is lower than that of its carrier. The ultrasonication method builds a platform for further study on the relations between the strength and the physicochemical properties of catalyst and carriers.