The surface plasmon device based on single-layer black phosphorous exhibits low light absorption. To address this issue, an anisotropic graphene-black phosphorus heterostructure plasmonicresonator is proposed, and the resonance spectrum and infrared sensing characteristic are studied. The designed graphene-black phosphorus heterostructure and asymmetric Fabry-Perot-like structure can improve the excitation efficiency of surface plasmons. It is found that the absorption of the proposed device can reach to 95.54% and 97.44% along x- and y-directions, respectively, by optimizing the thickness of dielectric layer of optical resonator. In addition, by changing the polarization direction of incident light to dynamically adjust the resonant wavelength, the maximum enhancement factor of 88 and 155 can be achieved for detecting v(COC)_s and r(CH₂)_a modes of polyethylene oxide molecular film with the thickness of 8 nm. The proposed anisotropic device with waveband tunable, high enhancement factor is expected to have the great potential applications in the detection of trace level samples.