Abstract: In this paper the interactions between air flow and particles have been investigated with a three dimensional particle dynamics analyzer (PDA) for the gas-solid two-phase flow in a horizontal boundary layer. The mean velocity and the statistics of turbulence fluctuations for both phases in the steamwise and the vertical direction were obtained simultaneously. Effects of particles with nominal diameter of 230μm at two different particle mass loading ratio, 1.8%and 24%, on the air flow boundary layer were exa...