In pH 30 Britton-Robinson buffer,sulfur chlorophenol N bonded with Cu(Ⅱ) to form a blue complex,and the complex reacted with protein to form a dark blue multi complex at room temperature which presents a maximum absorption at 724 nm and a red shift of 174 nm comparing with that of sulfur chlorophenol N.A new method for the determination of proteins was established based on the reaction of multi compound substance.The spectral characterisitics of the system and its influencing factors were investigated.Under the optimal conditions,the apparent molar absorptivity and linear range for HSA were 306×105 L?mol-1?cm-1 and 20-120 mg?L-1,respectively.With the presence of polyoxyethylene octyphenyl ether(OP),the sensitivity of the method could be increased by 31%.The mehtod was applied in the determination of urine protein with satisfactory results.And the sensitivity of the method is 16 times higher than that of the Biuret method.