The present invention relates to a method and an apparatus for generating an index for an encrypted field in order to protect private information in database. The method for generating the index for the encrypted field according to an embodiment of the present invention constructs an index as encrypted data itself without decrypting and storing contents of the encrypted field, constructs an index using distance information between encrypted data and a pre-configured reference value when the index is constructed, calculates a distance value from the reference value even when a search is performed, and performs a search by comparing the distance value with constructed index information table. In particular, when duplicated data exists, the present invention configures the duplicated data as a set of lower leaf nodes for a leaf node, thereby minimizing a search time.