Abstract: Progressive cavity pump (PCP) is a kind of devices extensively used in oilfield production. The PCP always runs under high temperature and in complex medium, which induces non-uniform thermal expansion and swelling of rubber stator of PCP. As a result, PCP’s running efficiency is reduced by the great changes of stator outline. The effects of thermal expansion and medium swelling on the change of the stator’s inner cavity outline are investigated by finite element simulations. A uniform thickness stator of PCP and the improvement of the stator’s inner cavity outline are proposed. Numerical results show that the proposed model can reduce the deformation non-uniformity of stator and running instability caused by thermal expansion and swelling. This research and the obtained results can be of great significance for new designs of stator outline of PCP in the special medium.