Abstract: Trace uranium was common precipitated by Fe-DDTC and determined with X-ray fluorescence. Uranium was common precipitated by 500 μg Fe and 10% DDTC in 0.01 mol/L nitric acid solution, then the common precipitation was transferred to filter paper as thin sample. The scatter line of Ag target is taken as internal standard line to revise the matrix effect and the float of the instrument. The line relativity coefficient of uranium curve is 0.9994 when the uranium mass concentration is 0.1-2.0 mg/L . Detection limit of uranium is 0.04 mg/L, which is one order of magnitude lower than X-ray fluorescence determined uranium solution.