The groundwater renewal ability is the basis for the rational development and utilization of groundwater resources, as well as the important factor to the grain production in Sanjiang Plain. The analyses of the shallow groundwater ages were conducted to study the recharge source of the groundwater and the renewable ability during 10th-17th, September 2009. There are 11 shallow groundwater samples were collected from the less than 60 m deep wells along Heilongjiang River, Songhua River and Wusuli River. The shallow groundwater samples were analyzed for concentrations of tritium (T) and chlorofluorocarbons (CFCs) by Quantulus 1220 and GC-ECD, respectively. The groundwater ages were calculated by the tritium and CFCs contents with piston flow model, respectively. The results show that the tritium content in shallow groundwater ranged from 1.7-61.2 TU. While, the CFC-12 and CFC-113 concentrations ranged from 0.04-1.25 pmol·kg^-1 and 0.1-0.71 pmol·kg^-1, respectively. The shallow groundwater age ranged from 39-51 years according to the contents of tritium. Meanwhile, the CFC-12 apparent groundwater age ranged from 38.2-61.7 years. The shallow groundwater with age less than 39 years was missing according to the tritium and CFCs data, indicating that the groundwater mainly recharged from the allogenic water in Sanjiang Plain. The percolating water from the water deep circulation recharges the surface water, forms to the wetland, and discharges to river finally. The groundwater table monitoring data shows that the groundwater table was the least in June since the agricultural irrigation. However, the groundwater table increased to the elevation before irrigation in September. The groundwater renewable ability also shows that there is stable recharge source in Sanjiang Plain. Consequently, the groundwater could be explored and utilized appropriately to increase the farmland, and to enhance the sustainable agricultural development in Sanjiang Plain.