Abstract: The present invention falls within the field of biotechnology, and specifically discloses a method for constructing a cyclized library and a ring-forming linker. The method comprises: 1) breaking a DNA sequence into fragments; 2) enabling two ends of the broken fragment to form 3? end protrusions; and 3) cyclizing the fragment with 3? end protrusions to form a ring-shaped library by means of a ring-forming linker, wherein the ring-forming linker is a double chain which is not completely paired and has 3? end protrusion at both ends, and the 3? end protrusion of the ring-forming linker is complementary to the 3? end protrusion of the broken fragment. According to the present invention, an A-sticky end of the end is formed by means of repairing the end of and the adding A to the broken DNA fragment, and same is then complementary to the specifically designed linker T sticky end to form a cyclized structure, and the connection at the gap is completed under the action of a ligase.