A photo-excited and polarization insensitive broadband tunable terahertz metamaterial absorber (MMA) based on the photo-sensitive material of silicon (Si) is proposed. The unit-cell structure of this MMA is consisting of compact split-ring resonator structure filled with silicon, mediate medium layer and metal ground-plane. The working frequency and absorption intensity of this terahertz MMA could be effectively tuned, when the conductivity of silicon was changed by the varied incident optical intensity. The simulation results demonstrate that this MMA is dynamically adjusted in the frequency range from 0.852 THz to 0.442 THz when the conductivity of silicon increases from 1.0×103 S/m to the 5.0×105 S/m. In addition, its relative bandwidth is as much as 63.37% and absorption modulation depth is up to 60.22%. The further simulation indicates that the MMA has characteristics of polarization insensitive and wide incident angle.