A method for forming an active region array and a semiconductor structure are provided. The method for forming the active region array includes the steps of: providing a substrate; forming a first mask layer on a surface of the substrate, a first etched pattern being provided in the first mask layer; forming a second mask layer covering a surface of the first mask layer; forming a third mask layer having a second etched pattern on a surface of the second mask layer; forming a flank covering a sidewall of the second etched pattern; removing the third mask layer to form a third etched pattern between adjacent flanks; etching the first mask layer along the third etched pattern to form a fourth etched pattern in the first mask layer; and etching the substrate along the first etched pattern and the fourth etched pattern, to form multiple active regions in the substrate.