PolQi2 is a PolΘ inhibitor that targets and inhibits alt-EJ (alternative end-joining) repair by inhibiting the helicase domain at the N-terminus of PolΘ. PolQi2 enhances the precision and integration efficiency of gene editing at different loci and in various cell lines. Furthermore, the combined use of PolQi2 with DNA-PK inhibitors reduces the off-target effects of Cas9. PolQi2 can be used in gene editing research.