Barrier patents refer to the existing patents which impede technology-based firms from commercializing their technology item. When barrier patents exist, a firm usually employs some strategic alternatives to cope with these commercialization-hindering patents, such as invalidation analysis, avoidance design and non-infringement logic. The present study focuses on the invalidation analysis among those alternatives and thus aims to developing a patent prior art search system for invalidation analysis of such barrier patents. Building on the patent database constructed using all patent registrations in the United States Trademark and Patent Office, this system recommends potential prior patents for validation analysis of a barrier patent, using three modules: 1) a user interest term definition module to organ-ize invalidation factors about a given barrier patent, 2) an information entropy calculation module to measure the amount of the user in-terests contained in each patent, and 3) a text similarity measurement module to calculate the relatedness between the barrier patent and any patent. We show the availability of this system by applying the system to real patent invalidation litigations. It is expected that this system will dramatically reduce the time and costs required for patent invalidation analysis and accordingly help researchers more concentrate on their own knowledge intensive tasks such as R&D planning.