The invention provides an automatic fluid preparation system for blood purification and a use method thereof. The system is provided with a fluid absorption pump, wherein concentrate is pumped by the fluid absorption pump from a concentrate vessel, is delivered to a liquid pipeline through a pipeline so as to mix with reverse osmosis water to form a mixed solution; the ion concentration of the mixed solution is detected by an ion concentration sensor, and is compared with a concentration target parameter value, if the concentration exceeds the standard, an alarm is given out, otherwise the rotating speed of the fluid absorption pump is regulated to control concentration pumping flow rate; and meanwhile, the rotating speed is compared with an alarm threshold value, an alarm is given out if the rotating speed is abnormal, otherwise, a liquid loop is detected in real time continuously. The invention has the advantages that the system has the function of ion concentration online detection and feedback control, can regulate the rotating speed of the fluid absorption pump in real time, effectively avoids safety risks of hemodialysis, avoids mechanical failures of a motor, and has high fluid preparation speed, accurate concentration proportion, high stability and high reliability.