Open microfluidics expands the possibilities of microfluidic operation in the applications that need energy or matter exchange during flowing. This paper reports the design, fabrication, and test of an open channel microfluidic chip for such kind of applications. The device is fabricated of polydimethylsiloxane (PDMS) soft lithography. And the open micro-channel is $50\ \mu\mathrm{m}$ wide, $80\ \mu\mathrm{m}$ deep and 4 mm long. By decreasing the outlet pressure, water-in-oil (WiO) two-phase flow has been successfully realized, and biological tests on yeast cells have verified the function of the open microfluidic chip.