Abstract: In order to predict the distribution and chemical behaviors of U, Pu, nitric acid in the Purex process of spent fuel reprocessing, a computer program is developed. The mathematical model of the program is based on quasi Newton arithmetic. The distribution profiles of 1A and 2D are calculated by the computer program, and the calculated results are in good agreement with the experimental results. A conclusion can be drown that the program shows better astringency and precision.