Spectral property is one of the basic properties of fiber lasers.With the increasing of the output power,the fiber nonlinearity has a significant effect on the high power laser system.On one hand,the spectral property is the direct characterization of the fiber nonlinearity and the damage effect;on the other hand,the spectral property of the fiber laser will affect the stability of the system and the relative devices.On the base of above reasons,we study the spectral property of the high power fiber laser t...