Porous Boron Nitride (BN) nanostructures have great advantages in the areas of energy storage, water cleaning and dye adsorption. Porous BN nanosheets have been prepared by a facile, one-step, template-free reaction using boric acid and urea as precursors in the N2/NH3 reducing atmosphere at high temperature. In order to control the morphology of BN nanosheets, a series of experiments by varying different parameters such as reactant ratio, temperature time, and gas flow rates were conducted. As a result, a synergy synthetic process for porous BN nanosheets were determined. BET analysis indicated that the specific surface area of the as-prepared sample was 735 m2/g with high pore volume of 1.24 cm3/g. To the best of our knowledge, the value of pore volume is the largest among the reports of BN porous materials.