The coming era of Web 2.0 focuses on users' active online participation and interaction. Among such interactive media, the blog is one representative tool of online knowledge construction. The purpose of this study is to explore the behavioral patterns and the depth of knowledge construction when using blogs for teachers' professional development. This research combines quantitative content analysis, sequential analysis, and qualitative protocol analysis. We studied how 470 teachers used blogs to conduct instructional knowledge interactions prior to the intervention of teacher educators and analyzed the teacher's behavioral patterns and the depth of knowledge construction. On the basis of the discovered behavioral patterns, we see that although blogs can serve as a channel for teachers to share teaching information, the aspect of knowledge construction is limited. We point out these limitations, and provide suggestions on how teacher educators can guide interactions during training. We also suggest how system developers can adjust blog functions to facilitate the discussion quality of online teacher communities. (Contains 2 figures and 5 tables.)