The invention discloses a method for knocking out MSTN (
myostatin) genes in a targeted manner by utilizing 
CRISPR-Cas9. According to the method, 
multiple species are subjected to homology comparison, two pairs of MSTN 
gene target sequences are selected, two pairs of 
DNA double strands which have the sequences different from the target sequences, the same 
expression protein and the same BsmBi sticky ends are synthesized according to the design principle of PAM of gRNA, the double strands are connected with pPDNA330 plasmids, a recombinant vector carrying MSTN homologous genes of 
multiple species is obtained and is used for detecting the 
gene knockout efficiency with a 
fluorescent protein expression method, carrier-transfected 
receptor cells, having higher knockout efficiency, of 
multiple species are selected, 
gene knockout and 
verification are performed, and simple, efficient and accurate 
gene knockout on the MSTN genes of the multiple species is completed.