This paper examines the role of metacognitive awareness in academic writing in a mixed-method study. In addition to validating an instrument assessing metacognitive knowledge and strategies in the context of academic writing, the study uncovered how Chinese multilingual students' metacognitive knowledge, metacognitive strategies, and metacognitive experiences influence their process of writing. A questionnaire was administered to 143 third-year undergraduate multilingual students and a semi-structured interview was conducted with 15 students. Through exploratory factor analysis and confirmatory factor analysis, a five-factor model was obtained, comprising metacognitive strategies (e.g. information management strategies and debugging strategies), metacognitive knowledge (e.g. declarative knowledge and procedural knowledge), planning, monitoring, and evaluating. The interviews suggested that metacognitive experiences (e.g. judgments and feelings) were shaped by learners' metacognitive knowledge, thus influencing their awareness of metacognitive strategies. The study contributes to a better understanding of the theoretical and pedagogical implications of metacognition in developing multilingual students' academic writing competence.