Abstract: Objective:To explore the signal changes of posttraumatic muscles and to study the relationship between pathological changes and MRI of muscle injury.Methods:Muscle injury models on 14 rabbits were set up and imaged with MRI several times after trauma.Randomly selected eight rabbits were sacrificed to obtain injured muscle tissue samples for light microscopic and eletron microscopic studies to compare with MRI.Results:The injured muscls showed high signal of T1WI and were kept more than 40 days.The pathological changes were hemorrhage,edema,degeneration,muscular necrosis,infiltration of inflammatotry cells.They are obvious on the 3rd day.The ultrastructlar changes were musclar fiber edema,mitochondrion enlargement,sarcoplasmic reticulum dilation and many high electronic density granules among muscular fibers.The peak of ultrastructural changes is during the 5th to 7th day and some abnormal changes are kept after 40 days.Conclusion:MRI is the best choice for muscle injury because of its close relationship with ultrastructural changes.