Transient hydrodynamics phenomena in the fluidized bed combustor (FBC) freeboard have been critical in the past two decades. Within a 152 mm ID FBC cold model, solid particle transient velocities were measured and analyzed with the assistance of advanced laser-based particle image velocimetry (PIV) instrumentation. Two layers of swirling secondary air were injected into the cold model. The PIV system was applied to the FBC cold model to visualize transient solid particle velocity. A series of transient solid particle velocity profiles were generated for the factorial analysis. In each profile, the solid particle velocity vectors (Vx and Vy) for 10 x 10 grids were generated Analysis of variance (ANOVA) was used to determine the significant factors that affect transient solid particle velocities, time, and position coordinates. Then, the 1010 factorial design method was used to develop a specific empirical model of transient solid particle velocity in the FBC freeboard, which was in the shape of V-x = f(1)(t, x, y) and V-y = f(2) (t, x, y). This unique factorial analysis method proved to be a very effective and practical method to evaluate experimental conditions and analyze experimental results in the FBC systems.