The invention relates to an online seabed scour-deposition dynamic real-time monitoring system, which is characterized in that a laser is connected with a circulator, the circulator is connected with an ordinary communication single-mode fiber, the ordinary communication single-mode fiber is divided into multiple sections, and a fiber grating is respectively arranged between every two adjacent sections; and the circulator is connected with a wavelength demodulator, and the wavelength demodulator is connected with a data processor. Due to the adoption of the online seabed scour-deposition dynamic real-time monitoring system, not only is the corrosion of seawater for sensors overcome and the cost reduced, but also the detection precision is also improved, the measurement precision can reach up to 0.3mm, a data signal can be transmitted to continental monitoring station within dozens of kilometers, the precise requirement for the existing seabed scour-deposition dynamic real-time dynamic monitoring can be reached, actual annual seabed scour-deposition variation is only sever centimeters to dozens of centimeters, and the problem of the real-time dynamic monitoring is solved.