The multi-modes hopping in Nd:YAG lasers induced by optical feedback is presented. The threshold gains of different longitudinal modes are modulated by optical feedback. The mode which has the lowest threshold gain can oscillate. During the tuning of the external cavity length, when the threshold gain of the oscillating mode is higher than that of the adjacent mode, mode hopping occurs, and the intensity modulation curve fluctuates correspondingly. The different positions of hopping modes in the gain curve lead to different mode hopping points and intensity modulation curves. The closer to the center frequency, the larger intensity amplitude and the longer oscillating period the mode has. When the frequencies of two hopping modes are symmetric about the center frequency, the intensity amplitudes of them are equal, and their oscillating periods are equal too.