A method of retrieving storage capacity of damaged sector. A storage medium comprising a storage capacity part and a reserved capacity part is provided. The storage capacity part comprises multiple primary sectors, while the reserved capacity part comprises multiple secondary sectors. The storage medium is scanned to find and record a damaged sector in the storage capacity part. An identity field of the damaged sector is overwritten by an null identity field of one of the secondary sectors. The identity field of the damaged sector is written into the secondary sector.