Abstract: Chemotherapy is irreplaceable in the treatment of malignant tumors.  Although combined chemotherapy has evident therapeutic efficacy on some malignant tumors, the curative effect is not quite satisfactory in most malignant tumors because of the multidrug-resistance (MDR) of the tumor cells to chemotherapy. Studies have shown that the occurrence of MDR involves a very complicated mechanism. It is caused by synthetic action that includes a variety of pathways, such as the cell membrane, cytoplasm, and the nucleus, which combines the effects of cell signal transduction, energy conversion, detoxification, and DNA synthesis among others. The mechanism of MDR remains unclear until now and, presently, several potential mechanisms have been proposed. Based on the multidrug-resistant mechanism of the tumor cells, some reversal agents, such as the calcium channel blockers, immunosuppressants, and protein kinase inhibitor, as well as Chinese crude drugs have been used and different effects have been achieved.