Tunable metamaterial absorbers play an important role in terahertz imaging and detection. We propose a multifunctional metamaterial absorber based on doped silicon. By introducing resonance and impedance matching into the absorber, a broadband absorption greater than 90% in the range of 0.8–10 THz is achieved. At the same time, the light regulation characteristics of the doped semiconductor are introduced into the absorber, and the precise amplitude control can be achieved in the range of 0.1–1.2 THz by changing the pump luminous flux. In addition, based on the principle of light-regulating the concentration of doped silicon carriers, the medium-doped silicon material is replaced by a highly doped silicon material, and a sensor with a sensitivity of up to 500 GHz/RIU is realized by combining the wave absorber with the microfluidic control. Finally, the broadband absorption characteristics and sensing performance of alcohol and water on the prepared device are verified by experiments, indicating that the absorber may have great potential in the field of sensor detection.