The invention relates to the field of nuclear auxiliary cooling water of one million-kilowatt nuclear power station, and provides a radiation protection method for expansion of spent fuel pool. The method comprises the following steps of: firstly, measuring and labeling the radiation intensity of the first grid; secondly, judging the measured values respectively according to the sizes of the firstpreset value and the second preset value; performing a first protection operation, a second protection operation or a third protection operation on the first grid by the judgment result, respectively; carrying out the radiation intensity level and the radiation protection treatment corresponding to the radiation intensity level on the first grid while following the ALARA principle. The radiationprotection method for expansion of spent fuel pool has the advantages that the radioactivity of the first grid is effectively reduced, the operation efficiency is high, the implementation is strong, the first grid is convenient to transport and the post-treatment process is convenient; the scheme fills the blank of the old grid removal process in the expansion operation of the spent fuel pool at home and abroad, and has certain reference value and milestone significance.