A method for transforming a droplet on a piezoelectric substrate into microfluid in a microchannel was presented and a microdevice for transforming the droplet was fabricated. The microdevice was comprised of a piezoelectric subdevice with two interdigital transducers on 128° YXLiNbO3 substrate, a poly(dimethylsiloxane)(PDMS) microchannel embedded into a printed circuit board and a steel needle with a small hole. The printed circuit board was hollowed out for embedding the piezoelectric subdevice and the PDMS microchannel using hollowedout technology.Surface acoustic waves excited by the two interdigital transducers on the piezoelectric subdevice were used to control the contact time of the droplet to the steel needle and then the volume of transformed microfluid. Transforming experiments of a water droplet into microfluid in the microchannel were done. Results showed that the droplet on the piezoelectric substrate could be successfully transformed into the microfluid in the microchannel, and the transformed volume was relied on the switching time of the electric signal applied to the two interdigital transducers. When the switching time was 9.667 s and fluid velocity was 0.365 μL/s, the transformed volume was 3.525 μL.