Abstract: Provided is a method for preparing a random sgRNA full-coverage group of a target sequence. The method comprises: cleaving a PAM region of a target sequence using a restriction enzyme; linking same to an sgRNA skeleton; acquiring a sequence targeting a protospacer region by means of a restriction enzyme site having a collateral activity on the sgRNA skeleton; linking same to a T7 promoter; acquiring an sgRNA library with the T7 promoter by means of amplification; and acquiring an sgRNA library of the target sequence by means of in-vitro transcription. Also disclosed are a method for preparing an sgRNA library of ribosomal RNA, a method for removing ribosomal RNA from the RNA library, and a method for removing human whole genomes from a host genome. The method has the advantages of low cost, simple manufacture, uniform coverage, low preference, no limitation on the length of a target sequence, no need for design of sgRNAs in large quantities, etc.