Objective To investigate the effects of Docetaxel combined with capecitabine on circulating tumor DNA (ctDNA) levels in patients with metastatic breast cancer. Methods A total of 82 patients with metastatic breast cancer in Hebi People’s Hhospital from October 2021 to October 2023 were selected and divided into groups according to lottery method. Forty-one patients in the control group were given capecitabine treatment, and 41 patients in the observation group were given Docetaxel treatment on the basis of capecitabine treatment. The disease control rate and ctDNA, carcinoembryonic Antigen (CEA), carbohydrate Antigen 153 (CA153) levels and adverse reactions. of the two groups were compared. Results After rigorous statistical analysis, the results showed that there was no statistical significance in the incidence of adverse reactions between the two groups (P>0.05). The disease control rate of the observation group was significantly higher than that of the control group. Meanwhile, the levels of CA153, CEA and ctDNA in the observation group were significantly lower than those in the control group, and the difference was statistically significant (P<0.05). Conclusion Docetaxel combined with capecitabine can effectively improve the anti-tumor effect of patients with metastatic breast cancer with high safety.