A silicon-on-insulator (SOI) variable optical attenuator (VOA) based on the plasma dispersion effect is optimized and realized, and the effects of doping concentration and distance about the VOA's modulation depth and attenuation efficiency are investigated. Two structures of the VOA component are designed to achieve low power consumption, high stability, and high modulation efficiency. The modulation depth of the series VOA scheme reached 60.11 dB, and the insertion loss is only 4.87 dB. Compared with conventional components, our optimized VOA can not only improve the modulation accuracy and efficiency but also reduce the wavelength dependence.