Hexagonal boron nitride nanofibers with high specific surface were successfully prepared through precursor pyrolysis method via boric acid, melamine and polyethylene glycol (PEG) as raw materials. The field emission scanning electron microscopy images showed that h-BN nanofibers were well aligned, and exhibited good fibrous structure. Chemical composition of the synthesized h-BN nanofibers was analyzed by X-ray diffraction, fourier transform infrared spectroscopy and thermogravimetric. Effects of precursor drying method and the PEG contents on morphologies and the specific surface area were investigated and optimized. Results indicated that the diameter of h-BN nanofibers increased with the ratio of boric acid to melamine, and their aspect ratios were greatly improved from 20 to 30 after freeze-drying treatment. Specific surface area of the h-BN nanofibers was increased from 65.25 to 319.07 m2/g due to the freeze-drying treatment. Besides, the content of PEG also obviously improved specific surface area. When the PEG content reached 2%, specific surface area of the h-BN nanofibers from the air-dried precursor was increased by 12.4 times to 874.58 m2/g. The resulted h-BN nanofibers show promising and potential applications in many fields including catalysis, hydrogen storage and environment.