The invention provides a micro-electro-mechanical device having differential capacitor of corresponding sizes, which includes a substrate; a top fixed electrode; a bottom fixed electrode; a mass, having a top electrode and a bottom electrode, wherein the top electrodes form a top capacitor with the top fixed electrode and the bottom electrodes form a bottom capacitor with the bottom fixed electrode; a top fixed electrode extension wall having an upper end connected to the top fixed electrode and a lower end connected to the substrate; and a bottom fixed electrode extension wall having a lower end connected to the substrate through the bottom electrode, wherein the bottom fixed electrode extension wall has no upper end connected to the top fixed electrode, and total areas of the top fixed electrode extension wall and the top fixed electrode facing the mass are substantially equal to total areas of the bottom fixed electrode extension wall and the bottom fixed electrode facing the mass.