This study designs a project-based flipped learning model for Business English Translation course and tests its efficacy by an empirical study on 65 third-year English major students divided into the experimental class and control class. This study incorporates the learning, teaching and assessment activities of both the students and teachers into a project-based flipped learning model by setting translation projects and dividing the students of the experimental class into a client group and three translator groups in each business translation unit. After one 16-week semester of experiment, this study conducts a post-test, questionnaires and interviews on both the experimental class and control class to test the efficacy of this new flipped learning model. The statistics and facts collected from the above-mentioned research methods suggest that the project-based flipped learning model can significantly enhance the students' motivation to learn out of class, stimulate their participation in class and raise their self-evaluation on translation competence. Additionally, this study finds that the traditional product-oriented summative assessment model is ineffective for Business English Translation course in a flipped-learning context. Therefore, this study tentatively proposes a process-oriented assessment model that is compatible to the flipped learning methodology so as to build integrated flipped classroom pedagogy with teaching, learning and assessment in a virtuous circle of mutual reinforcing.