Promoting the interactions among participants in an online-community is catching attention web sites' owners. In this paper, we first introduce Inference Diffusion Model (IDM), a method for discovering influential comment, participants and terms from threaded online discussions, and evaluate the performance by precision and recall measurement. Then we propose a new method for profiling participants in an online-community by expanding the idea of IDM. The positioning maps derived from the profiles clearly show the relations of participants as well as their characteristics.