Enhancing thesis quality is a central concern in higher education quality assurance. This study examines the effectiveness of an expert review mechanism in addressing this challenge. Using a comparative design, we analyzed data from 1,507 graduates without expert review (control group) and 452 graduates who underwent expert review (experimental group) at an open university. Results indicate that the control group’s thesis quality remained stable, while the experimental group showed a significant increase in thesis defense pass rates following the implementation of a closed-loop expert review mechanism based on the PDCA cycle. Scores across all five core dimensions of the "Bachelor’s Thesis Grading Standards"—including topic significance and academic norms—improved significantly, with particularly marked gains in traditionally weak areas such as academic standardization. The study confirms that the expert review mechanism effectively strengthens thesis quality control in open education by: (1) enabling early diagnosis and identification of deficiencies through preliminary assessment; (2) enhancing corrective effectiveness through specialized feedback; and (3) standardizing evaluation benchmarks through calibrated scoring. These findings provide empirical support for establishing a thesis quality assurance system tailored to the distinctive context of open education.