Abstract: Human thoracic injuries under blast loading are critical in individual protection research. The lungs, as the most vulnerable thoracic organ to blast injury, pose the most direct threat to life. Therefore, understanding pulmonary injury mechanisms is essential for guiding chest protective structure design. A blast shock wave–induced thoracic injury model was established using the THUMS biomechanical model and the LBE–ALE algorithm. Its reliability was validated against blast experiments conducted with the HSTM50 anthropomorphic test device. Using this model under a typical fatal-level blast scenario, the evolution and dominant mechanism of pulmonary injury were analyzed. A chest protective structure was then developed based on the identified injury mechanism, employing multilayer buffering energy absorption and an acoustic impedance gradient as the core protective strategy. Its performance was quantitatively evaluated using peak sternum velocity and acceleration as the primary injury criteria. Structural optimization was subsequently performed via a multi-objective framework to achieve a balance between protective performance and lightweight design. The results indicate that stress waves generated from the high-speed impact of the anterior chest wall against the lungs are the primary cause of pulmonary injury. The proposed protective structure effectively mitigates the blast-induced damage to human thorax. Compared to the unprotected condition, it reduces the peak sternum velocity and acceleration by 30.89% and 76.65%, respectively, lowering the injury severity from fatal to severe. Furthermore, the optimized design further reduces the peak sternum velocity and acceleration by 10.46% and 56.47%, respectively, achieving a moderate injury level.