Abstract: As a passive control strategy, nonlinear energy sink (NES) shows a strong broadband vibration reduction performance. However, how to effectively apply it to engineering practice remains to be studied. In order to realize its potential engineering application, a nonlinear energy sink based on spring geometric nonlinearity is proposed, which has controllable linear and nonlinear stiffness. The implementation scheme of the nonlinear energy sink is described, and the nonlinear control equation of the system with nonlinear energy sink is established. In the solution process, the complex variable averaging method and numerical method are used to solve the dynamic characteristics of the system. The vibration reduction performance of the nonlinear energy sink under harmonic excitations is evaluated by the basis of the amplitude and energy dissipation rate of the main system. The dynamic characteristics of the main system under different parameters and initial conditions are explored using time history diagrams and phase diagrams. The results show that by reasonably controlling the system parameters such as NES mass ratio, spring stiffness, damping, and the nonlinear energy sink can effectively suppress the resonance amplitude of the main system. By changing the additional mass of the nonlinear energy sink, the state of the main system in the resonance zone presents periodic response, strong modulation response, and chaotic response. Under different initial conditions, the main system has a variety of steady-state responses.