Disclosed herein are a system and method for recommending repeat-purchase products using modified self-similarity. The system is operated by a computer in an environment in which user equipment (UE), a database, and a web server are connected over a network. The system includes: a user information reception unit configured to receive user information from the database when the UE connects with the web server; a modified self-similarity calculation unit configured to calculate a modified self-similarity (MSS) using the user information received by the user information reception unit; a similarity calculation unit configured to calculate the sums of similarities between products by substituting the modified self-similarity, calculated by the modified self-similarity calculation unit, into an inter-product similarity calculation matrix; and a product recommendation unit configured to align the sums of similarities between products calculated by the similarity calculation unit and to transmit product information fulfilling preset criteria to the UE.