Objective To compare the effectiveness and mechanical differences in the dynamic hip screw (DHS), proximal femoral nail antirotation (PFNA), and proximal femoral internal fixator (PFI) for fixing complex unstable proximal intertrochanteric fractures by biomechanical testing. Methods Eighteen Synbones of the proximal femur were made to simulate complex unstable femoral intertrochanteric fracture models (Evans-Jensen TypeⅢ), which were fixed by DHS, PFNA, and PFI, respectively. The models were tested using a biomechanical testing machine, in order to compare their differences and advantages for fixing fractures. Results Under the compressive loads of 300, 600, and 1 200 N, the fracture displacement of the DHS was the maximum, with a significant difference compared with PFNA and PFI (P<0.05). There were no significant differences between PFNA and PFI (P>0.05). Under torsional loads of 300, 600, and 1 200 N, the torsional displacements of DHS and PFNA at the fracture ends were the maximum, with no significant difference (P>0.05). There were significant differences between PFI and PFNA as well as PFI and DHS (P<0.05). Conclusions For complex unstable proximal intertrochanteric fractures, the stability of the compression resistance of the PFI system is similar to that of the PFNA system. However, the torsional resistance of PFI is stronger than that of PFNA. The DHS system shows the least resistance with respect to compression and torsion.