This paper used cellulase method to extract R-phycoerythrin and purified it. A fluorescence method for detecting the content of Cu2+ was established based on the fluorescence quenching of R-phythrocytin by Cu2+. The results of the study showed that the concentration of R-phycoerythrin extracted by the cellulase method was 43.64 mg/mL when the extraction temperature was 40 ℃， the extraction time was 5 hours， and the amount of enzyme was 2.5%. Purification of phycoerythrin by using 60% ammonium sulfate precipitation and DEAE Sepharose FF column to obtain pharmaceutical grade R-phycoerythrin with a purity of 2.1， and this R-phycoerythrin had good selectivity to Cu2+. The best detection conditions were R-phycoerythrin concentration 1.2 mg/mL， water bath temperature 30 ℃， reaction time 15 min， buffer pH 7.0. There was a good linear relationship between relative fluorescence intensity and Cu2+ concentration in the range of 0.5~50 μmol/L Cu2+， and the lowest detection limit (S/N=3) can reach 0.06308 μmol/L. This method was applied to the detection of Cu2+ content in actual samples， and the sample recovery rate was 94.50%~106.03%. This method has the advantages of green safety， short detection time， high sensitivity， good selectivity， Etc， and the detection of heavy metal Cu2+ content in aquatic products has broad application prospects.