The generation of digital micro-fluid is indispensable operation unit for lab-on-a-piezoelectric-substrate. A new generation method of digital micro-fluid is proposed in this paper. An interdigital transducer (IDT) and a reflector were fabricated on 1280 YX-LiNbO3 substrate, which was used to excited surface acoustic wave. A needle with 400um inside diameter connected with a syringe was on the piezoelectric substrate, of which space could be adjusted. The needle tip and the piezoelectric substrate were coated with Teflon AF 1600. Water was used to generate digital micro-fluid experiments due to most samples or reagents being water solution. Experimental results show that the volumes of generated digital micro-fluid are relied on the space between the needle tip and the piezoelectric substrate, contact angle of the needle tip and RF power acted on the IDT. When the flow velocity of the syringe being 2.269 mm/min, space between the needle tip and the substrate being 0.98mm and 34mdB RF signal power, the volume of the generated water digital micro-fluid is 2ul. Change the space and RF signal power, the volume of generated water digital micro-fluid is also different. The method of generating digital micro-fluid can be greatly useful for Lab-on-a-piezoelelctric-chips.