This study examines Chinese primary science teachers' professional learning experience in a web-based community of practice established and run by practitioners, with support from teacher researchers. Over time, it has grown into a preferred knowledge-sharing base for primary science teachers of the region and gradually gained national recognition. Through narrative inquiry, we reconstruct a story that shows how the community emerged and developed into a way of empowering Chinese primary science teachers in their own professional development. Adopting the community of practice framework (Wenger 1998) and with attention guided by the metaphorical space of temporality, sociality, and place, our analysis brings out how the external contexts, the organizational features, and the teachers' learning practices intertwined and contribute to the long-lasting success of this community. Some of the key organizational features we identify go beyond the ones stressed by the existing literature. More importantly, we show the critical role external contexts can play in the working mechanism of a web-based community. On that basis, we suggested the need to enrich the methodological choices and broaden the scope of this line of research.