A low-cost simple preparing method for nitrogen-doped porous charcoal with a high specific surface area is disclosed. The method is characterized in that a characteristic that soybean meal absorbs water and then expands is utilized; a pretreating method in which soybean meal is soaked with a KOH solution is adopted to fully mix the KOH that is an activator and the soybean meal that is a precursor, thus achieving an objective of reducing the using amount of the activator; the specific surface area, the pore structure, the nitrogen content, and the like of the porous charcoal are adjusted and controlled through changing a plurality of process parameters, such as activation temperature (600-900 DEG C) and activation time (0.5-2 h); and the nitrogen-doped porous charcoal with the high specific surface area is prepared under a condition that the using amount of the activator is low.