An HPLC method has been developed to determine polydatin in giant knotweed rhizome.  In order to systematically validate the method, specificity, precision, linearity of reference solution and test solution, repeatability, reproducibility, accuracy, stability and robustness were measured.  In the robustness test, a one-variable-at-a-time procedure was applied to evaluate the influence of slight variations in method factors, including the flow rate, the column temperature, the extraction time, and etc., on the assay result of polydatin.  No significant differences were found when the process parameters changed during the experimental domain.  And system suitability test limits were defined based on the robustness test.  Results showed that the developed method was accurate, reproducible and robust.