The invention provides a light polarization state adjustment chip based on a waveguide grating coupler, comprising the following parts: a first waveguide, for inputting a light source to a 3dB beam splitter; two second waveguides, for connecting the 3dB beam splitter and thermo-optic modulators; two third waveguides, for connecting the thermo-optic modulators and optical attenuators; two fourth waveguides, for connecting the optical attenuators and mode converters; a 3dB beam splitter; two thermo-optic modulators; two optical attenuators; and a waveguide grating coupler having two input ports,wherein the two mode converters are located at the two output ports of the waveguide grating couplers. The devices of the light polarization state adjustment chip based on a waveguide grating couplerprovided by the invention can be integrated on the same substrate based on the optical waveguide devices, which has high integration degree, and is expected to be applied to the fields of optical communication, and on-chip/inter-chip optical interconnection.