Effect of ultrasonic on fermentation of microorganism makes cell membrane damage and has an increase of cell membrane permeability, and the membrane allows matter within to leave and that outside to enter the cell. When the power of ultrasonic is appropriately low, the cell can be retreated by themselves. Owning to this effect on fermentation, it can promote the cell growth, at the same time, can accelerate the secondary metabolite biosynthesize. As a result, the fermentation time is shortened and the production cost is reduced. This paper summarizes application of low ultrasonic in fermentation of microorganism and discusses its potential mechanism.