Abstract: In order to overcome difficulties in the recovery of historical tritium concentration in the determination of shallow groundwater age by the method of mathematical physical model,this paper,just taking the expo1atianal model as the example,deduces a new formula to calculate the groundwater age based on the equation of the tritium mathematical physical and the tritium analysis results in different times.This method is of significance both to overcome the difficulties in the recovery of the historical tritium concentration and to enhance the accuracy of age-dating.A case study from Yinchuan basin shows a good result and the mean age of shallow groundwater in Yinchan basin is about 30 years.