Deaf and hard of hearing (DHH) students face great challenges in becoming proficient readers. Vocabulary knowledge is consistently considered to be an important factor affecting DHH students’ reading ability. However, the mechanism that underlies the relationship between vocabulary knowledge and reading comprehension in DHH students remains unclear. Thus, the aim of this study was to determine the roles of word segmentation and reading fluency in the contribution of vocabulary knowledge to Chinese DHH students’ reading comprehension. A battery of tasks were administered to 116 Chinese DHH students from Grades 4 to 6 (mean age = 14.66 years). The results showed that vocabulary knowledge contributed to reading comprehension significantly in Chinese DHH students, and word segmentation and reading fluency played mediating roles in this relationship. Besides, the chain mediation effect of word segmentation and reading fluency was also significant. Revealing these mechanisms, which underlie the relationship between vocabulary knowledge and reading comprehension, is helpful to tailor remediation for DHH students.