Abstract: Based on the current situation of catalyst small particle content in renewable wet flue gas desulfurization absorption liquids after settling and filtering could not be determined accurately by traditional methods, laser particle size analyzer was tried to measure the small particle content in liquid, and the test conditions such as the amount of sample, the amount of internal standard and the range of the particle size distribution of the internal standard, were studied. The results show that the suitable conditions of test were as follow: sample was added to make the indication of PIDS detector reach 35, then 0.1 g internal standard was added, and the range of the particle size distribution of internal standard should be more than 100 μm. The method is easy and simple with good repeatability and high accuracy.