A membrane circuit structure with function expandability is provided. The membrane circuit structure includes a substrate, a lower circuit layer and a covering layer. The substrate includes a first region and at least one second region. The at least one second region is arranged near the first region. The lower circuit layer is printed on the first region. The lower circuit layer is made of a first conductive material. The covering layer is electroplated on a portion of a surface of the lower circuit layer. The covering layer is made of a second conductive material. At least one expansion line is welded on the corresponding second region, and electrically connected with the covering layer and a corresponding function-expanding unit.