Abstract: In order to study the flow pattern of Argon and the behavior of biomass particles in a horizontal entrained pyrolysis tube, a set of transparent cold flow test system was designed. Firstly, Particle Image Velocimetry(PIV) was introduced to carry out the measurements of Argon flow in the tube, and the oil fog was used as tracer particle. Secondly, at the same Argon flow rate, the behavior of biomass particles was studied by PIV. The results showed that the Argon velocity was fully developed after passing the 400 mm tube length, at Re=1695, the velocity profile was symmetric pattern, but quite different from the laminar parabola profile and most likely the turbulent flow regime. At the same Argon flow rate, the velocity of biomass particle was not symmetric, the max velocity at center line was much less than that of Argon flow, the biomass particles were accelerated all the time.