Safety release sub

The utility model relates to a safety releasing sub which comprises an upper sub (1), a releasing cylinder (2), an outer cylinder (4) and a limiting piston (3) which are distributed up and down, and first key groove limiting structures which are inserted up and down and are in rotation stopping fit are arranged between the lower end of the upper sub (1) and the upper end of the limiting piston (3). A second key groove limiting structure which is inserted inside and outside and is in vertical guide moving fit and rotation stopping fit is arranged between the outer wall of the releasing cylinder (2) and the inner wall of the limiting piston (3), and the first key groove limiting structure and the second key groove limiting structure are used for preventing the upper connector (1) and the releasing cylinder (2) from rotating relatively. On the basis of a differential pressure type mechanical releasing sub, a double-key-groove limiting structure with an anti-rotation function is additionally arranged, the safety