The 12 segments of pUC19 DNA/MspI (HpaII) marker have been separated and theoretical explanation was provided. The results gave better insight into the mechanisms of separations in polymer solutions. The dependence of different parameters on DNA size, electric field and the polymer concentration was evaluated and explained. Ogston model and a linear model were used to explain the behavior of 26～147 bp DNA fragment at lower electric field intensity. But, a new linear model was established in our experiment, which included the negative linear relation of electrophoretic mobility with DNA size. It could explain the separation mechanisms of 190～501 bp DNA fragment. The data should help to optimize and direct the small and medium DNA molecule separation in capillary electrophoresis and have a great sense in analysis of the mutational site of the tumor and the product of PCR.

Key words: high performance capillary electrophoresis, non-gel sieving, DNA, poly(ethylene oxide), separation model