Objective: To systematically explore the change of fixation stiffness (50-7500 N/mm) on the healing outcomes of seven different types of fracture (A1, A2, A3, B2, B3, C2, C3) under the OTA/AO fracture classification.Methods: Based upon an intramedullary nail fixation model of long bone fracture, we combined strain-regulated tissue differentiation theory with fuzzy logic algorithm and finite element analysis.Results: moderate fixation stiffnesses (e.g., 1500-2500 N/mm) shortened the healing time while ensuring recovery of the biomechanical performance of the fractured bone. However, the appropriate fixation stiffness for each fracture type is different. The sensitivity of the healing outcomes to the change of the fixation stiffness was also different between different fracture types. For type A fracture, a fixation stiffness of 1500 N/mm was associated with an optimal biomechanical recovery of the fractured site while the change in fixation stiffness had a large effect on healing; for type B and C fractures, the change in fixator stiffness above 1500 N/mm did not appreciably affect the healing results.Conclusions: Therefore, the fracture healing outcomes are affected by both the fixator stiffness and fracture type. When treating fractures in clinic, the selection of fixators should carefully take into account of fracture types.