An automatic liquid preparation system for purifying blood and its usage method. The system is provided with suction pumps (3,5). The suction pumps (3,5) suck concentrated liquid from a concentrated liquid container (7,8), and the concentrated liquid is transported into a liquid conduit (9) via a pipe to form mixed liquid with reverse osmosis water. The ion concentration of mixed liquid is detected by an ion concentration sensor (4,6), and the value of the ion concentration is compared with that of the target concentration parameter. If the concentration exceeds the standard value, an alarm is provided； if not, the rotation speeds of the suction pumps (3,5) are adjusted so as to control the suction flux of the concentrated liquid, and the rotation speed is compared with the alarm threshold simultaneously. If the rotation speed is abnormal, an alarm is provided； if not, the liquid circuit is detected continuously in real time. 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.L'invention concerne un système automatique de préparation de liquide pour épurer le sang et son procédé d'utilisation. Ledit système est pourvu de pompes d'aspiration (3, 5). Ces pompes d'aspiration (3, 5) aspirent un liquide concentré dans un contenant de liquide concentré (7, 8), et le liquide concentré est transporté par un tuyau jusqu'à un conduit de liquide (9) pour former un liquide mélangé avec de l'eau d'osmose inverse. La concentration ionique du liquide mélangé est détectée par un capteur de concentration ionique (4, 6), puis la valeur de la concentration ionique est comparée avec celle du paramètre de concentration cible. Si la concentration
