A forming method of a semiconductor structure includes providing a semiconductor substrate including a first zone having a plurality of separated storage grid structures and a second zone having a plurality of gate structures. First grooves are arranged between adjacent storage grid structures and second grooves are arranged between adjacent gate structures. The width of each first groove is smaller than that of the second groove. A liner layer is formed on the semiconductor substrate. The method also includes etching the liner layer for making the width of the top part of each first groove greater than that of the bottom part of each first groove; forming a second wall material layer on the liner layer; etching the second side wall material layer, forming a second side wall on the surface of the side wall of the gate structures and forming a medium layer filling the first grooves at the same time. By adopting the above method, the semiconductor structure forming technology can be simplified.