English writing teaching in senior high school is an irreplaceable way to improve students’ language literacy and expressive ability. The traditional English writing teaching model neglects students’ cognitive activities in the writing process, and the application of scaffolding instruction in actual contexts of English writing teaching in senior high school makes up for this deficiency. Scaffolding instruction is based on constructivism and the zone of proximal development theory, which advocates that teachers or adults with solid professional ability should participate in learning activities with students and provide external support to help them complete tasks. The application of scaffolding instruction in English writing teaching in senior high school emphasizes students’ initiative in mastering writing knowledge and skills, significantly improving students’ ability to construct knowledge and write independently. This paper analyzes the practical problems and reasons for implementing scaffolding instruction in English writing teaching in senior high schools and puts forward relevant solution strategies to provide valuable references for the current practice of English writing teaching in senior high schools in China.