The invention discloses a sonar technology-based oily deposit automatic identification method and system. The method comprises the steps of establishing an oily deposit acoustic image feature sample library, wherein the sample library comprises different simulation results, different type features and typical image features of an oily deposit; detecting the oily deposit, extracting related acoustic data to obtain sonar data, and displaying a sonar image; according to a display result of the sonar image, processing the sonar image to obtain sonar image features of the oily deposit; according to the sonar image features of the oily deposit, in combination with a sea-bottom deposit environment and an environment in which an oily deposit target exists, performing judgment, and performing manual pickup on a typical oily deposit sonar image; calculating a matching degree between the typical oily deposit sonar image and a sample image in the oily deposit acoustic image feature sample library; and according to a matching degree result, identifying the distribution position, shape and range of the oily deposit to obtain a first identification result. The method and the system have the advantages of quick identification, convenient use and accurate identification of the oily deposit.