In this book, an over view to the discrete and continuum model equations of double-stranded and double-helical is presented. They are formulated, via the transverse, longitudinal or torsional motions. Some new continuum models were constructed. The Stability analysis of some soliton of DNA dynamics model were studied via singular Sturm-Liouville Eigenvalue Problems. It was shown that the soliton wave is unstable. Thus under small disturbance dissociation of bases or the deterioration of the DNA membrane may occur.