Abstract: As an ideal tracer and radio element for dating, Tritium is broadly applied in hydrogeology. In order to obtain the tritium concentration in precipitation in northwest Tarim basin, a model is developed using factor analysis method and corrected with the measured data. The calculated results of model are in good agreement with the measured data, showing that the model is reasonable. The recovered tritium concentration data in precipitation in the northwestern Tarim basin is put to the piston flow model and the mixed flow model to date four groundwater samples in the study area. It is found that the tritium age results of groundwater are consistent with the hydrogeological conditions of study area, indicating that the model of tritium concentrations in precipitation in the northwestern of Tarim basin is reliable.