Multimode Brownian osicillater model of material molecules is set, and the method to calculate the three-pulse photon echo signal is discussed. The model of the Multimode Brownian oscillator is used to analyze the vibration of the Nile blue molecules and the vibration of the Nile blue molecules is regarded as the weighted coupling result of the Gaussian, overdamping, inhomogeneous and underdamping models. Changing the weight of these four models to alter the correlation function of the Nile blue molecules, we numerically simulate the three-pulse photon echo signal. Experiment about the three-pulse photon echo of the Nile blue ethanol solution is conducted. The concentration of Nile blue ethanol solution is 8×10-5 mol/L, the wavelength and the pulse width of the femtosecond laser light source are 623 nm and 40 fs, respectively. The three-pulse photon echo signal is measured to discuss the vibration model of the Nile blue molecules.