Abstract: A method was developed for determination of valence and concentration of uranium and plutonium in 1BP solution. Absorbance spectrum is exploited in determining the concentration of uranium and plutonium which coexist in several different valences. The molar absorption coefficients of uranium and plutonium in different valences and different wave lengths were fitted by slope method. By which, a mathematical model based on multiple linear regression(MLR) was evaluated for analysis of Pu(Ⅲ), U(Ⅳ), U(Ⅵ) and Pu(Ⅳ) in 1BP solution. A series of synthetic solutions which mixed up different concentration of uranium and plutonium solution were prepared for validating the method. The results show this method has great advantages of determining the valence and concentration of uranium and plutonium in 1BP solution: that Pu(Ⅲ) can be determined in range of 0.50-8.00 g/L and the recovery is 94.5%-103.9%, U(Ⅳ) can be determined in range of 0.45-38.15 g/L and the recovery is 95.3%-104.7%, U(Ⅵ) can be determined in range of 0.45-38.59 g/L and the recovery is 96.5%-103.0%. The relate standard deviation of all the measuring results are less than 3.0%(n=6). The recovery of total plutonium is 87.2%-100.6%. In a word, the method is simple, fast, highly sensitive and non-destructive.