OBJECTIVE Explored the causation of a case of incomitant vertical strabismus accompanied with elevation deficit and globe retraction by surgery. METHODS Case report. Orbital imaging study of MRI was used to discover the anatomic feature of extraocular muscle. By released the restrictive structure to treat strabismus. Histopathologic inspection was used to confirm the origin of the abnormal structure. RESULTS Abnormal extraocular muscle that located within the cone formed by the four recti muscles was the causation of strabismus. It arose at the annulus of Zinn, passing forwards between the inferior rectus muscle and lateral rectus muscle, and insert directly on the sclera. After Released it from eyeball and recession of inferior rectus muscle the strabismus was improved. Elevation deficit was not improved. Histopathologic inspection confirmed that the structure was muscular in origin. CONCLUSION The abnormal structure that found by MRI was the cause of elevation deficit and globe retraction. Its histopathologic inspection confirmed the muscular origin. The abnormal structure was an accessory extraocular muscle. For incomitant vertical strabismus accompanied with elevation deficit and globe retraction anomalous orbital structures maybe the causation. Orbital imaging studies should be done to explore the origin of disease.