The iron base catalyst residue in Fischer-Tropsch synthetic oil is one of serious issues which has to be paid close attention to in process and quality control.The method for accurate measurement of trace iron in Fischer-Tropsch synthetic oil becomes a crucial concern in process improvement.Several different test methods were compared in present research，and combust ashing samples from Fischer-Tropsch synthetic oil with different boiling points were tested by ICP-AES to determine their total iron trace content.The key procedures for the measurement were optimized.The conditions for Fischer-Tropsch synthetic sample pretreatment were optimized as follows:weighing 5 g of the sample,and ashing it with muffle at 500 ℃ for 1 h.The recovery for iron by this method was larger than 95% with relative standard deviation no more than 5.7%.The limits of detection and quantitation were 0.15 mg/kg and 0.50 mg/kg,respectively.