Background: Spelling is a prevalent strategy to teach children to read. However, research on the mechanism underlying the contribution of spelling to reading comprehension in Chinese children is limited. Methods: The primary aim of this study was to investigate the concurrent and longitudinal associations between spelling and reading comprehension and further test the mediating role of word reading fluency with 127 Chinese children (M[subscript age] = 76.01 months). Children were required to perform the tasks of nonverbal intelligence, expressive vocabulary, morphological awareness, phonological awareness, orthographic awareness, spelling, word reading fluency and reading comprehension at Grade 1. Then, reading comprehension was measured again 1 year later at Grade 2. The concurrent and longitudinal mediation models were fitted to the data by structural equation modelling. Results: The results showed that spelling was related to reading comprehension concurrently, and it predicted reading comprehension 1 year later while controlling for nonverbal intelligence, age, expressive vocabulary, metalinguistic awareness and the autoregressive effect of reading comprehension. Moreover, word reading fluency played mediating roles in the influence of spelling on reading comprehension in the concurrent and longitudinal models. Conclusions: These findings provided evidence that spelling is an important factor of reading comprehension and shed light on the nature of this association, highlighting the role of word reading fluency in linking spelling and Chinese children's reading comprehension.