To investigate biomass devolatilization characteristics heated by solid heat carriers at high heating rate， experiments on the velocity field of biomass particles were conducted with particle image velocimetry (PIV) during the flowing of ceramic balls and pulverized biomass powder in a vertical pipe. Based on the PIV experimental results, the calculation method of residence time of biomass particles was determined. Flash devolatilization experiments of corn stalk were performed with a down flow tube reactor heated by ceramic ball heat carriers at 400℃, 450℃, 500℃ and the char was collected at the drop distance of 100 mm,400 mm, 700 mm, 1200 mm of the tube, respectively. The devolatilization percentages of the char were analyzed with ash tracer method. Results indicate that the experimental data have excellent repeatability, but the data are not agreement with the model well. The experimental data coincide with the model to great extent when the movement function of the biomass particles is involved in computation of the models. 