Abstract：Objective To investigate the effects of different ion concentration and crowding agent on the torsional structure and mechanical properties of double DNAs braiding. Methods Taking 10 kb DNA as the research object, the effects of different concentrations of Na+, K+, Mg2+, polyethylene glycol (PEG) and different forces on the extension of the twisted braid of double DNA were investigated by the flow chamber experiment of magnetic tweezers. Results The double DNA twist superhelix is sensitive to metal ion concentration but insensitive to PEG. With the increase of ion concentration, the braids’ extension changes more gently with the rotation number, and the electrostatic shielding saturation concentration of the Mg2+ is much lower than that of the monovalent cation. The effect of crowded environment on DNA was mainly compression. The twisted structure of DNA is more stable under high force (4 pN ), and the structure fluctuates greatly under low force(2 pN). Conclusions The structure and mechanical properties of the superhelix produced in DNA replication are affected by the solution environment. The results may contribute to elucidate the mechanism of chromatin torsional torque affected by solution environment, and provide reference for the function of topoisomerase under different solution conditions.