In this study, fluorescent copper nanoclusters (Cu NCs) have been efficiently synthesized in a novel strategy via sonochemical method, using N-acetyl-L-cysteine (NAC) as reducing and stabilizing reagent. The preparation of Cu NCs could complete within 15 min due to the ultrasonic radiation treatment. The obtained NAC-Cu NCs exhibited red fluorescence at λ 630 nm. Silver ions could significantly induce fluorescence quenching of NAC-Cu NCs. Subsequently, a detection method for Ag with high response sensitivity and selectivity was constructed. The proposed method displayed a good linear relationship in the Ag concentration range of 1.64 × 10-1.16 × 10 M. The limit of detection (LOD) was as low as 7.76 × 10 M (signal/noise = 3). In addition, the practical application was further evaluated with environmental water samples, and the tested results were compared with those obtained by the inductively coupled plasma mass spectrometry (ICP-MS) method. The satisfactory recoveries (98.50%-101.6%) showed that the fluorescent detection method had potential application in environmental monitoring field.