This study is seeking for a model for Knowledge Management in project based firms. These firms used to try for awarding project from clients and deliver it with especial duration and budget. According the type and specification of projects they will achieve and/or create some knowledge which is mostly tacit. Most of the time, according to their obligation for delivering project on time, this tacit knowledge do not transfer to explicit ones and many times because of most of their knowledge workers are project-loyal, these firms will lose their acquisitioned knowledge through ended project. This study according to the literature reveals that KM can act as powerful instrument for increasing project-based firms’ performance and hence make more chance for them to award new projects. Of course this is a bilateral relationship; clients will have more trust to those firms who learn more from previous projects and firms will have more chance to award while they control all knowledge earned from previous projects.