In order to explore the new mode of using residual oil, Ansai oilfield first used horizontal wells to encrypt the remaining oil, and 7 key technologies and field tests were carried out. Based on the different way of encryption horizontal well spacing and the transformation parameter study, the mechanism of remaining oil distribution was obtained and the technology of using remaining oil in high and medium water-bearing encrypted horizontal well adapted to Ansai low permeability reservoir was explored. It is proved that horizontal encryption can effectively use the remaining oil and low abundance reservoir between wells to utilize the remaining reserves of developed areas, which provides new enlightenment for the same reservoir to further improve the recovery rate.