Abstract: Based on a proposed model that the growth of mean bubble diameter along the height of bed is proportional to average degree of bubble separation in the level, and a lot of existent experimental data, it has derived that the following calculation equation for bubble growth along the height of bed In addition, based on a simplified model of initial bubble diameter that is proportional to vertical centric distance of two adjacent bubbles, and the existent experimental data, the calculation equation of initial bubble diameter DBO was obtained- According to the obtained equation and the assumption that the bed expansion in a bubbling fluidised bed caused by existence of bubble only, the calculation equation of expansive height of bubbling fluidised bed was presented.