In this paper, a bi-functional Aluminum MEMS spatial light modulator (micromirror) device design is introduced. The bi-functional mirror can work in both torsional and piston modes, depending on the voltage applied to the bottom driving electrodes. The mirror was fabricated with thick photoresist sacrificial layer technique. The working principle and performance of the micromirror aer analyzed. Based upon the analysis, an optimized micromirror design is proposed. The mirror can deflect for a maximum displacement of 1.3μm in its piston mode, and rotate for a maximum angle of 3.1° in its torsional mode. The micromirror can be used to modulate the phase as well as the direction of the incident light due to its bi-functional modes.