Polarization-sensitive photodetectors based on two-dimensional (2D) materials have shown more attractive application prospects compared to traditional thin-film photodetectors due to their atomic thickness, tunable bandgap, high mobility and strong light–matter interactions. Among them, 2D molybdenum disulfide (MoS₂) has drawn numerous attentions in photodetection due to its wide spectral range, remarkable photoresponsivity and fast photo-switching rate. However, the isotropic crystal structure of MoS₂ hampers its application in the polarization-sensitive detection, which is highly desired in military and civilian applications. In this paper, we demonstrated an integration of plasmonic nanocavity with monolayer MoS₂ to achieve high photoresponsivity and polarization-sensitive photodetector. With the significant enhancement of electromagnetic field provided by the gap-surface-plasmon (GSP), we achieved a significant photoluminescence (PL) enhancement of 24-fold. Relying on the enhanced light absorption by our plasmonic nanocavity, which generally facilitates photo-generation of electron–hole pairs in MoS₂, we achieved a high photoresponsivity of 1.88 A/W and degree of linear polarization (DOLP) of 0.8 at the excitation wavelength of 633 nm. Our work provides a feasible and universal solution to realize polarization-sensitive photodetector of MoS₂ for high-performance and polarization-sensitive photodetectors.