To reduce the amylose content in rice, the core promoter region of the Wxb gene in japonica rice was targeted and edited by CRISPR/Cas9 gene editing technology to finely modulate the expression level of the Wxb gene. A target site (designated S7) near the TATA box element in the Wxb gene promoter was selected, and a CRISPR/Cas9 gene editing vector was constructed. Homozygous mutant lines were screened and obtained through Agrobacterium-mediated genetic transformation of the japonica rice cultivar DNPB. RT-qPCR was performed to detect the transcriptional expression levels of the Wxb gene, and agronomic traits as well as rice quality were evaluated. Field experiments were conducted to investigate the main agronomic traits, and quality analysis was employed to determine the amylose content of the rice grain. The result showed that compared with the wild type, the expression level of the Wxb gene in homozygous mutants was significantly reduced. No significant differences were observed in the main agronomic traits. The amylose content of rice grain in five mutant lines was 13.6%-16.6%, which was significantly lower than that of the wild type. In summary, targeted editing of the Wxb gene promoter region could effectively down-regulate the expression of the Wxb gene and subsequently reduce the amylose content of rice grain without affecting the basic agronomic traits of rice.