Abstract: To research the principle of feeding powders using vibrated capillary tube in theory, the movement behavior of the capillary tube under the excitation of the simple harmonic vibration is studied based on the physical model of vibrated capillary tube. The wave equations and displacement equations are deduced for the mechanical wave generated and transmitted on the capillary tube and the mass point of capillary tube wall, respectively. The decaying progressing wave generates and transmits when the incident wave is influenced by the reflected wave, and the mass point of the capillary tube wall moves elliptically. The obtained principle of feeding powders using the capillary tube shows that the powders flow from capillary under the action of movement of the mass point of the capillary tube wall, gravity and the interaction of powders. The influence of vibration amplitude on the acceleration of powder particles is studied. The results show that the acceleration increases with the increase of vibration amplitude, and the rate of micro-feeding powder increases with the increase of vibration amplitude. The theoretical results agree with the experiment results obtained by YANG Yong，TAKANO Takehiro, etc.

Key words: Amplitude, Capillary, Micro-feeding powder, Ultrasonic vibration