Learning to solve arithmetic word problems is an essential part of the primary school mathematics curriculum. The success of word-problem solving was previously found to relate to reading comprehension ability of children. However, the relationships between specific reading comprehension component skills and word-problem solving remain largely unknown. The current study examined the role of four comprehension subskills -- morphological, syntactic, inference making, and comprehension monitoring -- in children's performance on word-problem solving. A total of 129 primary four, Chinese-speaking, children participated in this study. Participants were assessed with tasks of comprehension subskills and arithmetic word problems, as well as two control measures (word reading and nonverbal Intelligence). All four comprehension subskills were found to have unique and significant predictions on children's equation formation performance. Furthermore, we proposed a model which described the relationships between the comprehension subskills and arithmetic word problems. The appropriateness of the hypothesized relationships was confirmed by path and mediation analyses. The present study not only provides evidences on the specific comprehension subskills that contribute to word-problem solving, but also provides practical implications for mathematics educators, and research insights for future word-problem studies.