The value of patent is shown in the technical contribution made by the patented invention beyond prior art. Such the technical contribution, along with the practice of the patent, will be transformed to the economic value in the market. Nevertheless, the occurrence of patent infringement breaks the ownership of the patentee over patent value, and eventually leads to illegal transfer of patent value to the infringer. In order to assess the objective scope on loss of patent value due to patent infringement, it is necessary to refer to the experience for practice of the patent by the patentee, as well as the result for patent infringement by the infringer. On considering the cost of information and administration resulting from patent infringement, assessment on damages for patent infringement is far from being exact. The adequate compensation through damages can’t be made on the ground of a compromise with the burden of aforesaid costs and arbitrary calculation. The advantage of the reasonable-royalty approach is established as a broad and flexible basis to calculate the damages from patent infringement, under the hypothetical negotiation, in accordance with the economic plan for the patent expected by the patentee and the infringing result produced by the infringer. Since the reasonable-royalty approach is significant but rarely adopted in the Taiwanese judicial decisions, the article tries to propose a workable model and related measuring factors for the future application of the reasonable-royalty approach in Taiwan by observing the comparative development of U.S. patent case law on reasonable royalties and the related academic literature. The article is expected to contribute a distinguished performance to the academia of patent law, and induce more deep-scale discussion in the issues on reasonable royalties.