The invention relates to the technical field of molecular biology, and discloses a reduced-representation genome library building method based on type IIB restriction enzyme digestion. The method comprises steps as follows: (1), digestion is performed on genome DNA by means of BsaXI enzyme; (2), an adaptor I and an adaptor II are connected for an enzyme-digested product; (3), a connected product is purified; (4), PCR (polymerase chain reaction) amplification is performed on the purified product; (5), a PCR product is purified to obtain a sequencing library, and two adaptors of the step (2) are synthesized through hybridization of two nucleotide fragments represented by sequences SEQ ID NO: 1 and SEQ ID NO: 2 as well as two nucleotide fragments represented by sequences SEQ ID NO: 3 and SEQ ID NO: 2 respectively. The library building method is simple, fast and low in library building cost, the built library has high accuracy, and high-throughput sequencing can be more effectively performed.