A contact window structure and a method for forming the contact window structure are provided. The method includes: an etching spacer is formed on a surface of a target layer, and a dielectric layer covering a substrate, the target layer and the etching spacer is formed; the dielectric layer is etched to form an etching hole in the dielectric layer, a bottom of the etching hole exposing a top surface of the etching spacer; and the etching spacer is removed along the etching hole to form an etching channel communicating with the etching hole, the etching channel exposing a portion of the surface of the target layer and constituting a contact window structure with the etching hole.