Forced vibration is an important teaching content in both college physics and college physics experiments.In order to make students understand the nonlinear characteristics of the forced vibration more deeply，the nonlinear correction of the forced vibration equation is carried out based on the nonlinear factors and experimental data involved in the Pohl resonator，and the nonlinear characteristics are discussed by numerical analysis. By introducing the Duffing equation of hard spring type，the evolution of the system from periodic motion to chaotic state is discussed. The relatively stable equilibrium point in forced vibration is compared with the singular attractor to expand the teaching content of nonlinear vibration.