Abstract: Static pressure，differential pressure and Poisson′s ratio of the rubber affect downhole motors′ output performance and mechanical efficiency greatly.This paper takes a 5/6-lobe downhole motor which is consumed the most as research object，and the forced state and deformation regularity of a downhole motor stator lining has been obtained by FEM analysis software firstly under an static pressure and then under an static pressure with a working pressure difference.Furthermore，the affection by Poisson′s ratio of the rubber is analyzed.The result shows that the deformation regularity is affected little by static pressure，but the deformation amplitude is affected more，and seriously affects the sealability；a working pressure difference can transform deformation regularity and deformation amplitude，but the influential action will be decreased as the inner pressure increased；a small change of Poisson′s ratio of the rubber can affect the deformation regularity seriously.Therefore，the rubber quality should be controlled strictly and Poisson′s ratio of stator rubber shuould be raised as much as possible.The research results can be applied to guide the selection of interference and optimize the design of linetype，so as to improve downhole motors′ working efficiency.

Key words: stator lining, sealability, static press &, pressure difference, FEM, optimal design中图分类号： 文献标识码： ADOI： X