While previous studies argue that BIM-based assembling collaboration promotes the communication and process management among participants in architectural design projects, it is still unknown which communication and socio-psychological factors are more and less activated in use of BIM-based collaboration. To investigate this research aim, in authentic BIM-used architectural retrofitting projects, the participants (N=36) collaborated and assessed the communication factors on (1) perceiving design results, (2)understanding partners'design intention, (3) proposing and converging opinions, the interpersonal design process management factors on (1) managing design process, (2) managing collaboration schedule, and the complementedness factors on (1) understanding partners' expertise, and comradeship. Statistical analyses reveal that the factor relevant to perceiving design results is better activated than the other factors (p<0.05), but all other factors are not much activated compared to perceiving design results. Deduced from the previous BIM studies and interviews, a reason roots in the shared forms and semantics of BIM. The shared semantics represent collaborators' information and allow the participants to perceive design changes explicitly. Meanwhile, BIM-based assembling collaboration is limited to represent observable, experience-able processes of design, and thus, several key socio-psychological factors, such as proposing and converging opinions and managing design process, are less activated.