The present disclosure relates to a method for detecting off-target sites of a programmable nuclease in a genome, and specifically, to a method for detecting off-target sites through data analysis by subjecting the genome isolated in vitro to programmable nucleases to cleave the genome and then performing whole genome sequencing or deep sequencing, and to a method for selecting on-target sites of a programmable nuclease, which minimizes the off-target effect, using this method. The Digenome-seq of the present disclosure can detect the off-target sites of a programmable nuclease on the genomic scale at a high degree of reproducibility, and thus can be used in the manufacture of programmable nucleases having high target specificity and the study thereof.