To explore the characteristic of lacrimal sac fossa on ESS and traditional maxillary operation, and to provide anatomy basis for the endoscopic endonasal dacryocystorhinostomy.Twenty-three heads of adult cadaver specimens were examined including the shape, direction and the thickness of wall of lacrimal sac fossa.The fossa is formed by the frontal portion of the maxillary bone and the lacrimal bone. The proportion of the frontal portion of the maxillary bone is bigger than the lacrimal bone. There is about 20 degrees between the rear wall of the fossa and the coronal plane.Before the endoscopic endonasal dacryocystorhinostomy we should scan the anterior portion of the medial orbital wall so that we can understand the anatomy of the fossa and improve the effect of the surgery.