The invention discloses an SOI-based MZI type 1*2 thermo-optical switch based on medium sedimentary type surface plasma waveguides. The SOI-based MZI type 1*2 thermo-optical switch comprises a silicon rib straight waveguide, a taper type silicon rib waveguide Y branch, six S-shaped silicon rib bent waveguides, the two medium sedimentary type surface plasma waveguides and a directional coupler of a silicon rib waveguide. The silicon rib straight waveguide serves as an interface of the SOI-based MZI type 1*2 thermo-optical switch and an external single mode fiber. The taper type silicon rib waveguide Y branch serves as a 3-dB optical beam splitter of the 1*2 thermo-optical switch and is used for equally splitting an input optical wave into two beams. The six S-shaped silicon rib bent waveguides are used for connecting the Y branch with modulating arms on the two sides, connecting the modulating arms with the directional coupler and outputting light modulated by the directional coupler. The medium sedimentary type surface plasma waveguides are located on the modulating arms on the two sides of the 1*2 thermo-optical switch and used for phase modulation of an MZI structure. The directional coupler is used for carrying out multi-mode interference on the two beams of light obtained after phase modulation and converting phase modulation into intensity modulation. The SOI-based MZI type 1*2 thermo-optical switch has the advantages of being fast in response, high in integration degree, low in switch power consumption and the like.