At different gas flow velocities and from two perpendicular directions, the particle size distribution and particle velocity distribution of a powder model for dry powder inhalers were investigated using the single frame and single exposure image method (SFSEI). The results were compared with those by the laser diffraction and numerical simulation methods. The applicability of SFSEI in the measurement of dry powder dispersion was analyzed. It is indicated that the measuring results are not sensitive to the particle quantity when it is no less than 750; the data obtained from vertical images are closer to the ones from the laser diffraction and the simulation results; the particle velocity measurement may be affected by the particle size. Based on this, it is shown that when applying the SFSEI method, the quantity of particles which are out of focus should be as less as possible to raise the measurement accuracy. Moreover, it is easier to achieve accurate results at lower gas flow.