A terahertz photo-excited tunable metamaterial sensor is investigated. It is composed of a hybrid metal-semiconductor structure (which is a split ring resonator (SRR)) and a flexible polyimide substrate. Silicon is filled in the gaps of the structure. Simulation results reveal that the conductivity of the semiconductor component can be tuned by changing the external pump light’s power, resulting in resonant peak shift of the composited metamaterial structure. The electric field and surface current density distributions of this structure under different resonant frequencies are also analyzed. The physical mechanism of this device has been further discussed. Moreover, the resonant peak will be red-shift as the concentration of the surrounding environment (calcium chloride, CaCl₂) increases, and the sensitivity is 11.4 GHz/M, which makes it a possible application in liquid sensing in terahertz region.