In this paper, an online theme-based collaborative learning model (OTBCL model) is proposed. Unlike the current approaches, the model takes into account the two aspects in learning: interpersonal socialization and mental internalization, and joins them with learning portfolios in learning activities of themes. Then, the architecture, user interfaces and learning portfolio module of OTBCL system are elaborately presented, some useful principles are summarized which guide the process of developing learning systems. Finally, a case study was introduced, which explains how to intuitively analyze the participation in group lifecycle with statistical diagrams automatically generated by the system.