A multi-band tunable terahertz metamaterial absorber is proposed. In the structure of the metamaterial absorber， a photosensitive semiconductor silicon material was added and a special top metal resonator was designed. Analyzed the influence of the parameters such as the opening length， line width and dielectric layer thickness on the absorption spectral characteristics of the terahertz metamaterial absorber. According to the relationship between illumination and the conductivity of photosensitive semiconductor silicon， the frequency tuning characteristics of the terahertz metamaterial absorber was studied. The simulation results obtain 12 absorption frequency modulations in the terahertz band， the absorption rate of 10 absorption peaks of them exceeds 90% near perfect absorption， and 6 absorptions rate up to 99% perfect absorption. Moreover， the absorptivity modulation depth and relative bandwidth reaches 85.9% and 85.5% respectively， with strong tunable characteristics. The photo excited terahertz metamaterial absorber has a simple structure， multi-band tunable and perfect absorption characteristics， and expands the application range of the absorber.