A method of forming aligned patterns on a mat contains steps of: (1). providing a main die configured to mold a body on a substrate; (2). forming multiple patterns on the body so as to produce a decoration portion; (3). forming a toothed cutting line on the body by ways of the alignment mark line so as to form multiple connection units on which multiple patterns are formed respectively, thus producing the mat; and (4). aligning the multiple patterns on the mat so as to provide or design the decoration portion on the multiple patterns, wherein the mat is disassembled to multiple coupling parts, and the multiple coupling parts of the mat are connected with another mat, thus producing an expandable mat.