In its broad sense, popular scientific knowledge could be divided into three levels, namely, the core layer, the intermediate layer and the peripheral layer. The core layer refers to the simplified scientific knowledge under a philosophy of “academic science”, complying with Merton's CUDOS Criterion. The intermediate layer represents post-academic scientific knowledge which is combined with manufacture and real life, complying with Ziman's PLACE Criterion. And the peripheral layer, is living scientific knowledge which is combined with society and culture, complying with Zeng Guoping's BASIC order. Each level has different characteristics by purpose, philosophy, content, pattern, physical performance and other aspects. There are no absolute boundaries among the three levels from the core to the periphery, but there is an obvious trend from “pure” basic scientific knowledge to culture-penetrated scientific knowledge. Detailed segmentation and deep analysis of popular scientific knowledge may provide science popularization work with theoretical implications.