This study focuses on the effect of a water-soluble copolymer, acrylic acid-oxalic acid-allylpolyethoxy carboxylate-8-hydroxy-1,3,6-pyrene trisulfonic acid trisodium salt (pyranine) (AA-APEM-APTA). APEM and APTA were copolymerized with acrylic acid (AA) to synthesize APTA tagged no phosphate and nitrogen-free calcium sulfate inhibitor AA-APEM-APTA. Structures of AA-APEM-APTA were evaluated by FT-IR and H-1-NMR, and oxalic acid, APEG and APEM by C-13-NMR. The observation shows that the dosage of AA-APEM-APTA plays an important role in CaSO4 inhibition. The performance of copolymer on inhibition of CaSO4 precipitation was compared with that of current commercial inhibitors. It was shown that the copolymer exhibited excellent ability to control inorganic minerals, with approximately 96 % CaSO4 inhibition. The relationship between AA-APEM-APTA's fluorescent intensity and its dosage was studied. The correlation coefficient R (2) of AA-APEM-APTA is 0.9999. The effect on formation of CaSO4 was investigated with a combination of scanning electronic microscopy and transmission electron microscope analysis. AA-APEM-APTA can be used safely in cooling water systems.