Metacognition has been identified as an essential component in the development of student writers' writing ability in multimedia environments. While the majority of available research in second language acquisition has investigated the beneficial effects of multimedia tools for raising students' metacognitive awareness on their writing, a limited number of studies have focused on the relationships between students' metacognition of their L2 writing processes and multimedia use; nor has any substantial study reported the effects of students' metacognitive awareness and multimedia use on their EFL writing. Given the significant role of metacognition and digital media in the learning of L2 writing, there is an urgent need to investigate this intersection. This chapter attempts to fill this gap by conceptualising, developing, and validating a new questionnaire framed within metacognitive theory to evaluate Chinese EFL student writers' perceived use of metacognitive writing strategies. In line with the theoretical understanding, the data collected through the questionnaire has resulted in a three-factor metacognitive structure of the Questionnaire on EFL Writers' Metacognitive Awareness of Writing Strategies in Multimedia Environments, which included advance planning before writing, elaborate monitoring during writing, and prompt evaluating after writing. The questionnaire based on this three-factor model was proven to be robust, with good construct validity and reliability, and it could be used as a reliable diagnostic instrument in teaching and learning English writing.