Abstract: Under the nonlinear binding forces the oscillations of a large floating gate are discussed. The harmonious oscillations with large amplitudes on the gate are discovered in the scale model.According to the structural feature of the floating gate, a nonlinear single - degree of harmonic oscillating model is set up. Due to the free vibration period of the gate is a function of the water level and gate opening, the,effect of the nonlinear binding forces is also a function of the same factors. The effect of nonlinear binding force on period and amplitude are also analyzed.