The invention provides a high-performance sgRNA and application thereof in gene editing. The sgRNA is shown as formula I, a target sequence transcribed RNA-modified sgRNA backbone (Formula I); the modified sgRNA backbone is an RNA molecule obtained by inserting an RNA fragment A between positions 14 and 15 of the sgRNA backbone and inserting an RNA fragment B between positions 18 and 19 of the sgRNA backbone; the RNA fragment A and the RNA fragment B are reversely complementary; both the RNA fragment A and the RNA fragment B have a size of 3 nt; the sgRNA backbone is an RNA molecule shown as asequence 9. Experiments prove that the modified sgRNA according to the invention can remarkably increase the C.T base substitution efficiency of a cytosine base editor (CBE), up to 86.4%.