The effect mechanism of project characteristics on the tacit knowledge transfer is studied. Idea generating activities and problem solving activities in New Product Development (NPD) are differentiated. At first, the main effect of project characteristics on the tacit knowledge transfer is inquired into and it is found that the team centralization has a negative relationships with the knowledge transfer, but other project characteristics play positive roles. Then how the task characteristics moderate the effect of project characteristics on the tacit knowledge transfer between the two activities in NPD is compared, and the different roles played by the task characteristics are discussed. At last, the research conclusion is provided.