3D elastoplastic FEM and the Partial Coefficient Method have been adopted to analyse the stress and deep anti-sliding stability of non-entirety and entirety polygonal line gravity dam. The results show that the entierly polygonal line gravity dam improved the stress and deformation conditions efficiently

but not always so efficiently in steady conditions. The above conclusion has been illustrated by load sharing between arch and beam. On the basis of these

preferable reinforcement has been put forward.