The technigue of Laser Doppler velocity measurement in two phase fluid depends on sui-table particles. How to select the scattering particles in two-phase flow measurement with 3-Dimentional Particle Dynamic Analyzer (3D-PDA)is discussed in this paper. The results show that the property of scat-tering particles is a main factor affecting the velocity measurement, and those particles with smaller size,lower density and higher refractive index are highly suggested for the seeding in turbulent flow measure-ments.