The invention discloses a one-dimensional boron nitride nanometer material and a preparation method thereof. The preparation method comprises the following steps: heating a one-dimensional borate precursor to 1000 to 1500 DEG C in a nitrogen containing atmosphere, carrying out a heat-preserved reaction, carrying out cooling to a room temperature in a protective atmosphere so as to obtain a crude product, and subjecting the crude product to after-treatment so as to obtain the one-dimensional boron nitride nanometer material, wherein the one-dimensional borate precursor can be selected from thegroup consisting of borate whiskers, nanorods, nanowires, nanobelts, etc. The invention has the following advantages: the preparation process is simple and controllable; raw materials are cheap and easily available; the conversion rate of the raw materials is up to 85%; the purity of a target product after purification is up to 99%; the one-dimensional boron nitride nanometer material with a weight of a gram or above can be prepared by a single-batch reaction; batch production of the one-dimensional boron nitride nanometer material can be realized; and the one-dimensional boron nitride nanometer material is favorable for being extensively applied to a plurality fields like deep ultraviolet illumination, composite materials, heat-dissipating materials, friction materials, drug loading, catalyst carriers, etc.