Optical fast-focusing device with liquid droplet excited by high frequency sound waves is a new MOEMS, which can be used in many fast optical imaging fields in miniature size. Some uncertain vibration characteristic about the test device is researched and revealed in this paper. First, the theoretical basis about the liquid droplet to form a fast-focusing lens in a hydrophobic capillary is represented. Then a test device of this liquid lens excited by an electronic loudspeaker is set up for preliminary experiments, and the vibration amplitude and frequency of the droplet under the effects of different technics parameters are measured and analyzed by orthogonal experiment method. Finally, the relative influence regularities and explanation are summarized for better developing this MOEMS or technology. The work in this paper will be a good start for our further research in fast-focusing liquid lens and its realization.