A variable optical attenuator (VOA) fabricated by micro mechanical technology is presented. Based on micro electromagnetic actuation, the attenuation level is adjusted by changing the radial offset between the input and output optical fiber. The structure parameter was determined through optics, mechanics and magnetic circuit analysis. The device was fabricated and packaged by micromachining technology. The packaged volume of the device is 20 mm×15 mm×8 mm. According to the experiment results, the insertion loss is less than 1 dB, the polarization relevant loss is less than 0.1 dB, dynamic range is larger than 35 dB and the driving voltage is less than 5 V. It promises to be a low cost, high performance passive device for all-optical-networks.