In this paper, we propose a light-excited, dynamically switchable, dual-band terahertz metamaterial absorber based on a square ring-wire structure. By adjusting the insulation/conduction state of photosensitive silicon and germanium chips embedded in the gaps of the structure, the absorber can be switched freely between three dual-band perfect-absorption states without changing its structure. The results show that when there is no laser pumping, the absorber works in a dual-band absorption state at 0.987 THz and 1.767 THz; when using 800 nm laser pumping, it switches to dual-band absorption at 0.717 THz and 1.444 THz; and when using 1550 nm laser pumping, it switches to dual-band absorption at 0.716 THz and 1.767 THz. In addition, the three switchable dual-band absorption mechanism is explained from equivalent circuit, impedance matching and current distributions, and the polarization-insensitive absorption characteristics are discussed.