A novel fluorescent-tagged scale inhibitor, linear-dendritic double hydrophilic block copolymer (acrylic acid (AA)/Allyloxy poly(ethylene glycol) polyglycerol (APEG-PG-(OH)n)/ 8-allyloxy-1, 3, 6-pyrene trisulfonic acid trisodium salt (PA) (MA/APEG-PG-(OH)n/PA) was synthesized by AA, APEG-PG-(OH)n and PA. Structures of APEG, APEG-PG-(OH)n and MA/APEG-PG-(OH)n/PA were carried out by 1H NMR. The observation shows that the dosage and the n value of MA/APEG-PG-(OH)n/PA plays an important role on CaCO3 inhibition. MA/APEG-PG-(OH)5/PA displays superior ability to inhibit the precipitation of calcium carbonate, with approximately 91% inhibition at a level of 8 mg/L. Relationship between AA/APEG- PG-(OH)5/PA‘s fluorescent intensity and its dosage was studied. Correlation coefficient R of MA/APEG-PG-(OH)5/PA's is 0.9991. The effect on formation of CaCO3 was investigated with the combination of X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis. MA/APEG-PG-(OH)5/PA can be used to accurately measure copolymer consumption on line besides providing excellent CaCO3.