The paper finds out poor engagement in business English training program prevents adult learners at College of Continuing Education of Guangdong University of Foreign Studies from improving their communication skills. PBL (Project-Based Learning) is proposed to motivate adult learners to get involved with learning a lot. Based on the perspective of psychology, learners' needs may produce motivation which drives learners to actively participate in learning. Integrating McGregor's Theory X and Theory Y and Maslow's Hierarchy of Needs to the implementation of PBL, the paper highlights teachers should stick to Theory Y, Participative Management Style which is suggested to more inspire learners. And then, through satisfying three classes of adapted needs: belonging needs, esteem needs and self-actualization, PBL can be employed to increase learners' participation, and thus improving their communication skills. The proposal sheds light on how PBL is effectively employed in business English teaching and learning from the perspectives of motivation management.