Disclosed is a waste water treatment system with a buffering device, the system comprising a waste water pretreatment device, an evaporator, a circulating crystallizer, a crystal filtration device and a water removal device which communicate with each other in sequence, and further comprising a primary buffering device and a secondary buffering device, wherein one end of the primary buffering device is in bi-directional communication with the circulating crystallizer, and the other end thereof is connected to the evaporator; and the secondary buffering device is in bi-directional communication with the circulating crystallizer. Further disclosed is a waste water treatment method for a waste water treatment system with a buffering device.