The present invention relates to a catalyst system for preparing a cyclic olefin addition polymer, a method for preparing the catalyst system and a cyclic olefin addition polymer prepared by the method, and more particularly to the method comprising the steps of contacting some content of norbornene-based monomer having a specific polar functional group with a catalyst system comprising a) a Group X transition metal compound; b) a compound comprising a neutral Group XV electron donor ligand having a cone angle of at least 160°; and c) a salt capable of offering an anion that can be weakly coordinated to the transition metal of the a) the Group X transition metal compound.