Using FE method, the typical honeycomb core modulus is studied, the nonlinear stress-strain relationship with a property of “harden spring” under tensile load and “soften spring” under compress load is obtained. The effect of the height of the core on the analysis of the modulus is discussed, the results are compared with these acquired from Gibson formula. The polynomial fitting method is adopted to get the nonlinear modulus. The Kirchhoff assumption and Galerkin approximation are used to get the equation of motion of the typical honeycomb core sandwich beam. The numerical results are obtained. The nonlinear amplitude-frequency response of forced vibration is discussed.