Abstract
Duffing harmonic oscillator is a common model for nonlinear phenomena in science and engineering. This paper presents He's Energy Balance Method (EBM) for solving nonlinear differential equations. Two strong nonlinear cases have been studied analytically. The analytical results of the EBM are compared with the solutions obtained by applying He's Frequency Amplitude Formulation (FAF) and numerical solutions using Runge-Kutta method. The results show that this method is potentially presented to solve high nonlinear oscillator equations.