Hierarchical ZnO nanostructures with the morphology of sleeve-fishes have been fabricated on Si substrate through vapor phase transport at 850 degrees C. Studies find that each nansleeve-fish is composed of a screw-shaped microrod and some tapering nanowires grown on the microrod, all of which grow along the [0001] direction. Photoluminescence spectra exhibits strong UV emission around 385 nm without any green emissions detected, indicating that the high-quality ZnO nanostructures with low level of oxygen vacancies are obtained in our experiment. Field-emission measurements on the nanosleeve-fishes show a turn-on field as low as 2.2 V/microm at a current density of 0.1 microA/cm(2) with a anode-sample separation of 600 microm, and the emission current density reached 1 mA/cm(2) at an applied field of about 5.8 V/microm. The excellent field emission properties from such kind of nanostructures make them promising candidates for further applications in FE microelectronic devices.