在Ahsan等给出的描述DNA分子弹性的两状态虫链模型的基础上，考虑到盐离子浓度对静电自由能的影响，得到了延伸力随盐浓度的变化规律，结果表明：在低力和高力范围延伸力受盐浓度的影响较小。相变延伸范围随盐浓度的增加非线性增加，与实验测量一致。

In this paper, we give the modified Ising-WLC model of double-stranded DNA molecules and study the force-extension curve as a function of salt concentration. The free energy is divided into the non-electrostatic and electrostatic portion that is related to the salt concentration in this model. The effects of salt on the electrostatic free energy are studied by a cylinder model in which DNA is considered as an infinitely long uniformly negatively charged cylinder and to be immersed in an infinite medium. It is shown that the overstretching force increases nonlinearly with salt concentration and the influence of salt on the force-extension curve is very little at below and above the overstretching force. These results are in agreement with the experimental measurements.