In the solution mining of rock salt, the deformation and development of rock salt cavity directly influence the safe and sequential mine production, so understanding and mastering of the shape change of the cavity is of great significance for guiding the mine production. In the light of various well-grouped controlled solution mining plan, the solution pressure at wellheads was measured in the No.1 well pattern of Yanhu Glauber Salt Mine, Yuncheng, and the shape of the cavities was analyzed by the finite-element back analysis method for seepage. The results of back analyses had shown that the rock salt cavities appeared as ellipses in plane and their opening heights were almost equal in vertical direction, which ranged from 6 to 10 cm, and the shape of rock salt cavities resulted from complex effects of dissolving and deforming of ore bed, and were all along in deforming and breaking .