The growth of wheat and sugar beet under salt stress and their uptake of salt were studied through greenhouse and field experiments. The salt tolerance of wheat was lower than that of sugar beet. Na⁺ inhibited the uptake of K⁺ and Ca²⁺.The relations between relative dry weight of wheat and sugar beet and soil salt content confirmed to the Maas-Hoffman model. Na⁺ contents in leaves of wheat and sugar beet had positive linear relations with the salt content of soil. Their relations with the relative dry weight of the crops also confirmed to the Mans-Hoffman model. According to these results, on the basis of Maas-Hoffman model between the Na⁺ content in leaves and the relative dry weight of crop, a method for the dynamic monitoring, diagnosis and prediction of salt injuries to crops was proposed. The predicted results about salt injuries to wheat and sugar beet in fields are satisfactory by this method.