Biomechanical forces are involved in the physiological function of molecules. Single molecule magnetic tweezers have been developed and used to investigate the mechanical properties of individual biomolecules and their interactions. In this review, we will mainly review the application of magnetic tweezers for the mechanical research of DNA at the single molecule level. Firstly, we will briefly introduce the fundamentals and the categories of the instrumental setups. Secondly, we will summarize and discuss the application of magnetic tweezers for the analysis of the mechanical properties of DNA and the interactions between DNA and different substances such as DNA-modifying enzymes, DNA structural proteins, cations, drugs, and organic chemicals. Finally, the advantages and disadvantages of magnetic tweezers for DNA research are discussed. This work will provide an important guide to the scientists in the field of DNA mechanics.