Abstract: This work designed a new uranium concentration on-line analysis system by using solid standard addition-γ absorption method. The calibrating table with different thickness metal slices were placed between radioactive source and sample flow-through cell. Different thickness metal calibrating slices are equivalent different uranium concentration. The structure of measuring module, inner standard material, on-line analysis flow path and analysis software had been designed and processed. The on-line analysis system was tested by using organic uranium solution. The results show that the system has a high accuracy with less than 3% relative deviation for uranium concentration. On-line measurement system has good stability with sr less than 1% within 72 h. This on-line analysis system is applicable to determinate the uranium concentration of complex matrix in nuclear fuel reprocessing.