The invention discloses an intermittent CRRT (Continuous Renal Replacement Therapy) machine capacity balance device. The device comprises a blood circulation system, a first liquid circulation system, and a second liquid circulation system, wherein the blood circulation system consists of a hollow fiber dialyzer, a liquid outlet pipeline, a first circuit interrupting device, a liquid pump, a displacement liquid / dialysis liquid container and a liquid return pipeline; the second liquid circulation system consists of an exogenous displacement liquid / dialysis liquid container, an exogenous displacement liquid / dialysis liquid container liquid outlet pipeline, a second circuit interrupting device, a liquid pump, a displacement liquid / dialysis liquid container, and an exogenous displacement liquid / dialysis liquid container liquid return pipeline; the first liquid circulation system is in contact with the blood circulation system to perform substance exchange; since the volumes are fixed, volume change is not involved in the process of exchange; the first liquid circulation system is separated from the blood system, and is connected to the second liquid system to perform liquid exchange to be refilled with clean fresh displacement liquid, and then performs solute exchange with the blood system. The process is repeated to fulfill the aim of continuously removing solute.