Online teacher professional development is a branch of online learning, which offers educators opportunities to refine their pedagogical skills and collaboratively construct knowledge within professional learning communities. During these interactions, teachers often engage in knowledge construction while exhibiting diverse role characteristics. Investigating these role characteristics and knowledge construction patterns can enhance the comprehension of the interaction process and contribute to online teacher professional development design, addressing challenges such as weak activity and low collaboration. This study examined the key roles that actively interact or contribute to the online community in online teacher professional development, analysing interactive participation characteristics and knowledge construction behaviour patterns. Data were collected from an online teacher professional development activity in China. Statistical, content and lag sequence analysis methods were employed. Results showed that the three key roles had weak interaction persistence and different content quality in interactive participation characteristics. Knowledge construction behaviours of key roles were generally at a high level, with different patterns observed. Finally, the study proposed practical implications based on key roles' interactive participation characteristics and knowledge construction behaviour patterns. These implications may inspire the learning designs that promote online interaction and deep learning based on role characteristics in online teacher professional development.