A method for splitting the aqueous droplet encapsulated by an oil droplet was presented in this paper. A microdevice on 128°YXLiNbO3 substrate has been developed for splitting the aqueous droplet encapsulated by an oil droplet. An interdigital transducer for exciting surface acoustic wave was fabricated on the 128°YXLiNbO3 substrate using microelectric technology. The aqueous droplet would be split by instantaneously decreasing the power of the electrical signal due to the inertia force from surface acoustic wave, while the oil droplet was not split due to greater surface tension than the acoustic radiation force. The theoretical analysis and splitting experiments of a blue aqueous droplet encapsulated by a paraffin oil droplet were carried out. Results showed that the aqueous droplet in the oil droplet could be successfully split when the electrical signal with 12.3 dBm was suddenly switched off.