Aggregation and crystallization of soluble salts is a critical contributor to the surface weathering, structural deconstruction and loss of strength of ancient bricks of the Great Wild Goose Pagoda in Xi’an, Shaanxi Province. In order to analyze the mechanism of the salt disease, we carried out a deterioration simulation where brick samples from the pagoda were soaked with a saturated solution of sodium sulfate. During the repeated cycles of crystallization-dissolution of thenardite (sodium sulfate), we determined the variation of mass, wave velocity, uniaxial compressive strength and other characteristics of the samples. The results show that 1) the weathering phenomena of the samples in the laboratory were similar to those of the natural bricks of the pagoda; 2) the continuous crystallization force of thenardite increased the porosity and loosened the inner structure of the bricks; 3) the variation patterns of mass, wave velocity and uniaxial compressive strength were similar—increasing at the beginning and then decreasing. The bearing capacity of a brick for soluble salts is 0.5% that of the mass percentage.