Abstract: The principal conditions of GCdetermination method for subnanogr-am Cr through Cr (Ⅲ)-trifluoroacetylacetonate were sdudied in detail. Aplan of balanced design was selectd for seven factors each with two modified conditions, such that the sensitive factors most likely to influence the results were picked out, improved and emphasized in the procedure. The analytical results for tap water were compared with neutron activation analysis. The coefficient of variation for 1 to 10 ppb Cr in water is ≤3% (n≥6), recovery is in the range of 95-100%, and the 3σ limit of detection is 0.014ppb (n = 22). Four batches of hair samples were analyzed, the Cr content is in the range of 0.42-2.18 μg/g and the coefficient of variation (n = 5) being 10-3% accordingly.