Popular scientific reading books, as the bridge between scientific academic research and general public's knowledge capital, could raise scientific literacy and facilitate comprehension for general public. Popular scientific reading books could attract children to read because of vivid exhibition of text and illustrating graphs. However, some scientific reading books are still too difficult for children to read since they are not designed for children particularly in Taiwan and reading capacity among children are heterogeneous. One promising education strategy is to recommend more scientific reading books corresponding to textbook lessons, which could raise children's interest in exploring science and further reading. In US, Lexile framework for reading has been developed and applied for English books to assist in more efficient and objective text leveling. For recent years, Chinese Readability Index Explorer (CRIE) has been developed for Chinese text. The main research question here is, for Chinese scientific reading books, whether there are differences in text leveling between system's (CRIE) and experts' identification. In our research, we invite teacher librarians to recommend popular scientific reading books, identify the grade levels, and assign these books to corresponding textbook lessons. We not only discuss the principles and criteria of experts' leveling, compare the different results between CRIE and experts' opinions, but also investigate the reasons behind these differences.