This study takes the initiative to use structural equation modeling (SEM) to explore the interrelationships among metacognitive knowledge, first language (L1) reading ability, second language (L2) proficiency and L2 reading comprehension. Data were collected using an L2 proficiency test, L1 and L2 reading tests and strategy questionnaires with 268 sophomore university students learning English as a foreign language (EFL) in China. The results showed that all three predictors had significant, direct, positive effects on L2 reading comprehension. Moreover, metacognitive knowledge exerted indirect effects on L2 reading by means of L1 reading ability and L2 language proficiency. The findings help to refine the framework of L2 reading and elaborate on the mechanism by which metacognitive knowledge facilitates L2 reading. These findings have significant classroom implications, including the integration of strategy instruction and L1 literacy resources into L2 curriculum.