The invention relates to food processing and storage technologies, and discloses an ultra-low-temperature liquid-nitrogen deep-cooling quick-freezing method of portunus trituberculatus. The ultra-low-temperature liquid-nitrogen deep-cooling quick-freezing method of the portunus trituberculatus comprises the following steps: (1), carrying out washing; (2), carrying out soaking, namely soaking the portunus trituberculatus in a low-temperature protective agent solution; (3), carrying out quick freezing, namely carrying out liquid-nitrogen quick-freezing treatment on the soaked portunus trituberculatus, wherein the liquid-nitrogen quick-freezing treatment is carried out in three stages; (4), carrying out ice-glazing; (5), carrying out vacuum packaging; and (6), carrying out cryopreservation. A three-stage gradual cooling process is adopted in the ultra-low-temperature liquid-nitrogen deep-cooling quick-freezing method of the portunus trituberculatus so as to ensure a small amount of ice crystal formation and low drying loss of the portunus trituberculatus after the deep-cooling quick-freezing treatment. The portunus trituberculatus treated by the ultra-low-temperature liquid-nitrogen deep-cooling quick-freezing method has relatively good low-temperature cracking resistance performance, and wholeness of product cells are preserved; moreover, original color, luster, freshness and flavor of the portunus trituberculatus are preserved, shelf life of the portunus trituberculatus is greatly prolonged, and freshness grade of the portunus trituberculatus is good. In addition, shell of the portunus trituberculatus after the deep-cooling quick-freezing treatment is not liable to crack.