Android is an operating system designed specifically for mobile devices. It has a layered architecture. In this paper, we extract Android's concrete layered architecture by analyzing the build dependency relation between Android sub-projects and use it to validate the proposed conceptual architecture. Our experiment shows that Android's concrete architecture conforms to the conceptual architecture. Apart from that, we also show the extracted architecture can help developers and users better understand the Android system and further demonstrate its potential benefits in studying the impact of changes.