Abstract: The present invention relates to a method for treating colorectal cancer (CRC); this present invention confirms that KRAS mutation CRC patients benefit from metformin more significantly for the first time and further confirms that the down-regulated expression of MATE1 in the discharge passage of metformin is a key mechanism for the sensitivity of KRAS mutation CRC cells to metformin. The transcriptional level of MATE1 is decreased and the concentration of metformin in tumor cells is increased by upregulating the transmethylase DNMT1 and down-regulating the demethylase TET1/2, and thereby the inhibiting effect of metformin on tumor cell proliferation is enhanced. The present invention provides a novel thinking and method for the treatment of colorectal cancer, which has profound significance and is worth popularizing energetically.