Abstract: The effects of NaCl solution on the swelling characteristics of bentonite with different initial water contents are investigated by performing a series of wetting tests and nuclear magnetic resonance tests. The test results indicate that when the initial content is less than 10%, the optimal T₂ do as not change with the increasing initial water content, and according to the relation between T₂ and the radius of water, the soil has only strongly bound water. That is to say, the strongly bound water content is about 10% for the bentonite, which is the similar to that by other methods, thus the nuclear magnetic resonance can determine the water content of strongly bound water. The wetting test results indicate that when the initial water is less than 10%, the NaCl solution has no effects on the swelling. When the initial water content is larger than 10%, the swelling strain decreases with the increasing NaCl solution concentration. The reasons for the above results are as follows: when the soil has only strongly bound water, it generates cationic hydration to increase in the fixed charge density of soil after immersed by the NaCl solution. It results in an increase in the swelling pressure, and thus results in the increasing swelling strain. The thickness of diffuse double layers and the swelling pressure decrease with the increasing NaCl solution concentration.