The hydrodynamic effects of varying operating parameters in the fluidized bed combustor (FBC) have been of great interest to the FBC design and manufacturing process. Some experiments to investigate the gas/particle flows in the gaseous fluidized bed were performed with the laser-based phase Doppler particle analyzer (PDPA). In the experiments, the PDPA was used to measure the vertical component of fluidizing particle velocitiy at one specific position point. The robust experimental design method was used to evaluate the experimental conditions and to analyze the experimental results. An empirical model for the particle velocity vertical component V-y with particle size (S) and fluidizing airflow rate (R) as variables was dei-eloped for the FBC cold model. From the model, it was found that vertical component V-y. has a strong linear relationship with the fluidizing airflow rate (R), while particle size (S) has less linear relationship to V-y. It can also be seen that V-y increased when fluidizing airflow rate increased and V-y decreased when particle size increased.