The paper reports the synthesis of a new fluorescent reagent 3-pheny1-5-(2′-carboxy1phenylazo)-2-thioxo-4-thiazolinone (3PRACP). The product has been purified by column absorption chromatography. Its conposition has been confirmed by elemental analysis, IR, HNMR and MS. We also studied its fluorescent properties At pH=5.6, 3PRACP can form a chelate with trace Cu2+and when λ ex/λ em=305nm/405nm, the fluorescence is very intense. The fluorescent intensity has a linear relationship with the concentration of Cu2+in the range of (0.1 – 48) × 10−9M. The sensitivity is 8X10−9. Using the method, we detected trace copper in pork and vegetable, with good results.