We developed a digital micro-fluid generator for the discrete dispensing of bio-samples into a bio-analytical unit on piezoelectric substrate. This micro-fluid device is comprised of a micro-channel, a step and a 1280 yx-LiNbO3 substrate. An ejector jet pump is used for offering a uniform linear velocity. After formed micro-fluid from micro-channel arrives the step, it will be down to the piezoelectric substrate due to its gravity and will be transported by surface acoustic wave (SAW). The micro-fluid generator can generate mono-disperse digital micro-fluid of micro-liter volume relied on the gap between micro-channel and the step. The generation time of digital micro-fluid is about several seconds time, which is also relation to the gap. And the digital micro-fluid generation is repeatable and stable with a typical variation of less than 7% of digital micro-fluid volume. Our digital micro-fluid generator can be effectively applied to biochemical analysis on a piezoelectric substrate.