Abstract: Tritium values and Cl-concentrations from groundwater in the bedrock aquifers and surface water are used to estimate quantitatively the input from precipitation in Beijing.The results indicate that the whole sampling recharge input is after the nucleus explosion,the Cl-concentrations in the Beijing plain region before near industrialization is about 6.8mg/L,the regional input value ranges from 6.8 to 20 mg/L.The relationship between 2H and 18 O suggests that in the Beijing Plain the altitude effect is more notability than the continental effect,and a contrast model for groundwater research in Beijing Plain is also provided.