An auto jartest analyzer includes a plurality of water sample reaction equipment, coagulant providing/controlling equipment and a coagulant concentration analysis device. The coagulant providing/controlling equipment provides coagulant of different concentration to the plurality of water sample reaction equipment to allow contaminants in a water sample of the water sample reaction equipment to precipitate. The coagulant concentration analysis device analyzes turbidity measurements for the plurality of water sample reaction equipment and determines if they meet predetermined analysis criteria, so as to figure out an optimal concentration of coagulant currently required to be added to the water sample. This thus achieves automatic analysis of an addition concentration of coagulant to be added to the water sample, which not only improves operational efficiency but also makes the analysis result more accurate.