A new triazene reagent，1-（2-benzothiazole）-3-（8-（5-p-sulfophenylazo）)quinolinetriazene（BTSPQT），was synthesized using 2-aminobenzothiazole and 5-p-sulfophenylazo-8-aminoquinoline as raw material，and the chromogenic reaction of this reagent with Cu2+was investigated.The results showed that BTSPQT could react with Cu2+ at room temperature in Na2B4O7-HCl buffer（pH 8.0） containing 0.3% Triton X-100 to form a purple complex with a molar ratio of BTSPQT to Cu2+ by 2∶1 and the stability constant of （2.59±0.40）×109.The maximum absorption wavelength of this complex was located at 610 nm.Based on this reaction，a new spectrophotometric method for the determination of Cu2+ was developed.Beer′s law was obeyed in this method in the concentration range of 0.025-0.40 mg/L for Cu2+ with the apparent molar absorptivity of 3.61×105 L?mol-1?cm-1.Some common metals at the concentration below 2.5 mg/L did not interfer the determination of 0.40 mg/L Cu2+.The proposed method was applied in the determination of trace copper in flour and tea samples with recoveries of 96%-103% and relative standard deviations（RSDs） less than 4.0%.