Abstract: Teaching diagnosis and improvement system is an effective measure to ensure the internal quality of vocational colleges. The student level is one of the five horizontal levels of “College, Specialty, Curriculum, Teacher and Student” in the basic framework of “Five Vertical, Five Horizontal and One Platform”, and is also the most direct basis for judging the effectiveness of teaching reform. By creating “Two Chains” to identify the logical starting point of diagnosis and improvement, according to the target chain and standard chain in advance, the monitoring and warning in the event, the diagnosis and improvement after the event, it realizes the transformation of student work in vocational colleges from the “Proving by others” of traditional assessment to the “Self-proving” of internal quality assurance. The internal quality assurance at the student work level starts from creating the student work target chain and standard chain,and creating the student personal target chain and standard chain, which are divided into two main lines,and ensures the quality of talent cultivation from the work route and the student personal growth route.The two routes have different starting points but the same destination, which are the concrete performance of quality culture in students’ work.