Objective To design a novel double-leaf proximal humeral locking plate for fixing greater and lesser tuberosities in complex proximal humeral fractures, and evaluate its fixing stability by biomechanical tests. Methods Twelve fresh-frozen humerus specimens with intact rotator cuff were randomly divided into two groups (Group A and Group B) to establish the same greater and lesser tuberosities fracture models. Specimens in Group A were fixed with the double-leaf proximal humeral locking plate, while specimens in Group B were fixed with the proximal humeral internal locking system (PHILOS) and tension band suture, and a 3.5-mm cannulated screw was added to stabilize the lesser tuberosity. The tensile test on subscapularis, infraspinatus and teres, supraspinatus as well as the load-to-failure test on greater and lesser tuberosities were performed on specimens in two groups. Results For subscapularis tensile tests, displacements under 150 N tensile stretch and after fatigue test in Group A were both significantly smaller than those in Group B (P<0.05). For infraspinatus and teres tensile tests, there were no statistical differences between Group A and B in displacements under 150 N tensile stretch and after fatigue test (P>0.05). For supraspinatus tensile tests, there were no statistical differences between Group A and B in displacements under 90 N tensile stretch and after fatigue test (P>0.05). For load-to-failure tests on lesser tuberosity, the failure load in Group A was significantly greater than that in Group B (P<0.05), and the failure displacement in Group A was significantly smaller than that in Group B (P<0.05). For load-to-failure tests on greater tuberosity, there were no statistical differences between Group A and B in both the failure load and failure displacement (P>0.05). Conclusions Compared with the ordinary tension band suture plus cannulated screw for fixing lesser tuberosity, the novel double-leaf proximal humeral locking plate shows more obvious biomechanical stability, with the advantage of simultaneously fixing greater and lesser tuberosities. The research findings provide a new choice for the clinical treatment of complex proximal humeral fractures.