The contact angles of droplets are measured by using the vertical shooting-diameter measurement method instead of the traditional lateral shooting-contour extraction-function fitting method. The measuring efficiency is improved because the process of function fitting is omitted. The theoretical formula for contact angles is derived. With the combination of computer with image processing technology, the edge contours of projected images of droplets are extracted and the diameters of these edges are measured. By substituting the diameter value into the derived theoretical formula, the contact angles of droplets are obtained. The relation curves of contact angle versus applied voltage obtained by the experiment and theoretical calculation are consistent, which confirms the feasibility of this proposed method.