The invention relates to a method for calculating maximum increment of rotor current of a doubly-fed induction generator in case of terminal voltage drop. The method is characterized in that subject to 'rotor exciting voltage and rotor speed remaining unchanged', a current transient process excited by terminal voltage drop in stator and rotor windings of the DFIG (doubly-fed induction generator) is analyzed scientifically and reasonably, a physical process and a rotor current incremental frequency component of the doubly-fed induction generator after terminal voltage drop are analyzed, and based on the superposition principle, the method for calculating maximum increment of the rotor current excited by terminal voltage drop while crowbar protection idles is provided; on such basis, the stator and rotor winding resistance is omitted, effectiveness of an analytical calculation model under fixed wind speed and different wind speeds is deducted and verified, and the method has the advantages of simplicity in calculation, quickness in calculation and the like.