We simulated the jammed finger using 3-dimensinal FEM and elucidated the mechanism of finger injury. We obtained CT and MRI images from the index finger in a fully extended position. The shape of the finger was extracted using a software and used to build a 3D mesh model. The 3D finger model was analyzed using a software. The 3D finger model was constituted of a distal phalanx bone, a middle phalanx bone, subcutaneous tissue, skin, a nail, tendons and ligaments. The condition of FEM was that a rigid ball collided against the finger model from three directions. As a result, The equivalent Stress was larger by the collision from the palm side better than that from dorsum side. As for this thing, the possibility that an mallet fracture produced by a collision from the palm side was suggested.