The invention discloses a silicon substrate middle-infrared band light modulator based on MEMS. Two sets of same waveguide structures are respectively etched on top layer silicon of an SOI material, wherein the two waveguide structure are composed of bent silicon waveguides, electrodes and bar-type silicon waveguides, the two sets of waveguide structures are oppositely and symmetrically arranged along the center of top layer silicon, one end of each bent silicon waveguide is connected with the corresponding bar-type waveguide, and the other end of each bent silicon waveguide is connected with the corresponding electrode. A row of air grooves formed at equal intervals are formed in a silicon dioxide substrate, the two bar-type waveguides are located above the air grooves, and the joints of adjacent grooves are used for supporting the two bar-type waveguides. By the adoption of the silicon substrate middle-infrared band light modulator, high absorption losses, caused by silicon dioxide layers, of the whole device are reduced, the bent degree of suspension waveguides can be controlled through the MEMS, the coupling length of a coupler can be changed, signals of the output end are controlled, and the thermo-optic effect is avoided. The silicon substrate middle-infrared band light modulator has the advantages of being simple in structure, compatible with the CMOS process, and easy to control.