The invention discloses a high-linearity degree-of-polarization quantum-well infrared detector with a plasmon micro-cavity coupled structure. The detector is composed of an upper metal grating layer, a quantum-well infrared photovoltaic conversion activating layer and a lower metal reflecting layer, wherein the upper metal grating layer is formed by metal strips. The detector has the advantages that under the mode selection effect of an electromagnetic wave near-field coupled micro cavity formed by plasmon resonance between the upper metal grating layer and the lower metal reflecting layer, photons capable of entering the micro cavity are mainly photons capable of achieving resonance with a detected wavelength polarization mode; the direction of electric vectors of the photons entering the micro cavity is changed to the z direction from the x direction by being modulated in a micro-cavity mode, and the photons can be absorbed by quantum-well sub-bands in a transition mode to achieve the photovoltaic conversion process. With the advantages, the polarization coupled structure can greatly improve the extinction ratio of polarization responses, and extremely-high polarization distinguishing capacity of the detector is achieved.