Abstract: Swelling capability is one of the key parameters for high-level radioactive waste disposal.The swelling capability of buffer material is closely related to the stability of repository function.It is important to predict and evaluate the swelling capability of bentonite accurately.In order to study the relationship between swelling capability of buffer material and dry density and effective montmorillonite content.Swelling pressure test of GMZ07 and GMZ24-200 bentonites immersed in deionized water is carried out, and swelling test of GMZ24-200 is also carried out.The results show that the swelling pressure increases with time, and the swelling pressure increases with dry density.The higher the dry density performs, the higher the initial swelling deformation of the specimen is, and the steeper the initial curve of the swelling pressure time history curve is.The swelling pressure curve of GMZ07 bentonite has a "double peak" structure at low density, but is not obvious at high density.The swelling pressure curve of GMZ24-200 bentonite has no "double peak".The montmorillonite content of GMZ07 bentonite is much higher than that of GMZ24-200 bentonite, which results in that the swelling pressure of GMZ07 bentonite in deionized water is greater than that of GMZ24-200 bentonite.The maximum swelling pressure and dry density of two kinds of bentonites are fitted, and the relationship between effective montmorillonite content and maximum swelling pressure is formed.The swelling deformation of GMZ24-200 bentonite increases with time, and there is a good linear relationship between dry density and maximum swelling deformation.