Precision medicine is to customize the treatment options for individual patient based on the personal genome information. Colorectal cancer (CRC) is one of the most common cancer worldwide. Molecular heterogeneity of CRC, which includes the MSI phenotype, hypermutation phenotype, and their relationship with clinical preferences, is believed to be one of the main factors responsible for the considerable variability in treatment response. The development of powerful next-generation sequencing (NGS) technologies allows us to further understand the biological behavior of colorectal cancer, and to analyze the prognosis and chemotherapeutic drug reactions by molecular diagnostic techniques, which can guide the clinical treatment. This paper will introduce the new findings in this field. Meanwhile we integrate the new progress of key pathways including EGFR, RAS, PI3K/AKT and VEGF, and the experience in selective patients through associated molecular diagnostic screening who gain better efficacy after target therapy. The technique for detecting circulating tumor DNA (ctDNA) is introduced here as well, which can identify patients with high risk for recurrence, and demonstrate the risk of chemotherapy resistance. Mechanism of tumor drug resistance may be revealed by dynamic observation of gene alteration during treatment.