Objective To evaluate the biomechanical advantages of medial support screws (MSSs) in locking proximal humeral plate for treating proximal humerus fractures. Methods Thirty synthetic left humeri were randomly divided into 3 groups to establish the fracture models. Group A was fixed with a locking proximal humerus plate with medial cortical support, but without MSSs; group B was fixed with 3 MSSs, but without medial cortical support; group C was fixed with neither medial cortical support nor MSSs. Axial compression, torsion, shear stiffness and failure tests were applied on the specimens of the three groups. Results For axial compression tests, the maximum load of group A, B, C was (240.88±19.13), (169.04±19.26), (128.58±17.53) N, respectively; the axial stiffness of group A, B, C was (424.4±101.2), (230.7±40.54), (147.0±29.2) N/mm, respectively, showing significant differences (P<0.05). For torsion tests, the maximum torque of group C was (7.57±0.53) N?m, which was statistically different from both group A((8.92±0.25) N?m) and group B((9.09±0.31) N?m, P<0.05), and the torsional stiffness of group C((1.53±0.10) N?m/(°)) was statistically different from both group A((1.80±0.07) N?m/(°)) and group B((1.86±0.07) N?m/(°), P<0.05), but no significant differences were found between groups A and groups B in the maximum torque and torsional stiffness(P>0.05). For shear stiffness tests, the maximum load of group A, B, C was (444.71±20.87), (228.79±28.95), (188.73±26.15) N, respectively; the shear stiffness of group A, B, C was (70.0± 54.4), (183.89±29.64), (140.2±32.1) N/mm, respectively, showing significant differences (P<0.05). For failure tests, the failure load of group A ((2 949.76±355.08) N) was statistically different from both group B ((2 448.13±402.39)N) and group C ((2 222.55±336.41) N) (P<0.05), but no statistical differences were found between group B and group C (P>0.05). Conclusions Using three MSSs in locking plate for proximal humerus fractures shows optimal biomechanical properties, as compared to the situation without restoration of the medial column support. The reconstruction of the medial cortical support or MSSs for proximal humerus fractures helps to enhance the mechanical stability of the humeral head and prevent failure after internal fixation.