In order to study changes in engineering properties of impervious soil with salt and to determine the critical value of salt content that conforms to design criterion, experiments were performed for testing physical, chemical, and mechanical properties of samples. These impervious soil samples were taken from river embankment and reservoir dam, and then they were mixed with various kinds and amounts of salt. The results show that the salt contents, in low liquid limit clay, all conform to the criterion with refined salt no more than 3.29％ and mixed salt no more than 2.99％. Within the tested salt content range, the permeability coefficients are all between 1×10^-7cm/s and 7.9×10^-7cm/s, which satisfy the criterion. Moreover, other indicators in experiments do change, but not much.