In this paper, an efficient process for preparing monodisperse gold nanoparticles coated with silica shells (Au@SiO2) was reported, and a novel DNA electrochemical biosensor based on layer-by-layer self-assembled technology as well as Au@SiO2 nanoparticles was presented. Chitosan was immobilized on gold electrode by good film-forming property and lots of amino because of strong electrostatic adsorption effect between amino and gold atom, Au@SiO2 nanoparticles were also immobilized to the electrode in that it kept the excellent features of gold nanoparticles, therefore, thoil group modified DNA (SH-ssDNA) probe sequence can self-assembled on Au@SiO2 nanoparticles modified electrode with the purpose of realize quantitative detection of complementary DNA. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were applied to investigate the electrochemical behavior of different modified electrodes with methylene blue as hybrid indicator. The results in optimization experiment condition show that: the peak current difference value pre and post hybridization was linearly related to the logatithmic value of the target DNA concentration ranging from 10-10~10-6mol/L. A detection limit of 4.02×10-11mol/L can be estimated.