MA–APEM–APTA detection limit is 0.79 mg/L according to the detection limit formula. Good relationship between MA–APEM–APTA fluorescent intensity and its dosage (the correlation coefficient R2 = 0.9973) ensures that MA–APEM–APTA is a valuable indicator for cooling water system performance. The new active polymer test method provides an easy, quick, and accurate method to determine polymer consumption.