Abstract: Hexafluoroisopropanol (HFIP) solution (mobile phase) containing 0.01 mol·L^-1 sodium trifluoroacetate was used as the solvent to dissolve the sample of p-dioxycyclohexanone (PPDO), to make the mass concentration of the sample reach to 4 g·L^-1. The sample solution was filtered with 0.45 μm filter membrane, and the separation was performed on the Shodex HFIP 805/Shodex HFIP 803 tandem columns of the gel chromatograph. The angle of the multi-angle laser light scatterer was normalized by the standard solution of polymethyl methacrylate (PMMA), and the detection was carried out on the target separated by the chromatograph. The increment of the refractive index measured by the differential refractometer was substituted into the formula for determining the absolute molecular weight by the light scattering method to calculate the weight-average molecular weight, number-average molecular weight and molecular weight distribution index of PPDO. As shown by the results that RSDs (n=6) of weight-average molecular weight, number-average molecular weight and molecular weight distribution index were all less than 5.0%. The molecular conformation of PPDO in HFIP was random line cluster. The weight-average molecular weight, number-average molecular weight and molecular weight distribution index obtained by gel chromatography were much higher than those obtained by the above method, mainly due to the large difference between molecular structures of PMMA (used for making the standard cure) and PPDO.