Tunable thermal absorber has become a research hotspot for new devices with high efficiency and low loss, which has a broad application prospect in the fields of infrared communication and material detection. A non-reciprocal thermal absorber composed of InP magneto-optical nanowire arrays is proposed, which can realize strong non-reciprocal absorption/radiation at ∼8 to 10 μm by utilizing the surface plasmon resonance and multiple reflections among the nanowires. The optical properties of nanowire arrays are closely related to their structural parameters. We analyze the effects of variables such as the diameter, length, shape, and period spacing of the nanowires and find that only the cylindrical nanowire arrays expand the band of non-reciprocal effects, creating a completely new non-reciprocal peak at 9.44 μm. The electric field energy distributions of different cross sections intuitively explain the enhancement mechanism of cylindrical nanowire arrays and the physical mechanism of the nonreciprocal effect. In addition, we compare the computational results of effective medium theory (EMT) with finite difference time domain and analyze the applicable conditions for fast prediction using EMT. Last, we explore the photothermal effect when the nonreciprocity of the array is maximized, and the results show that for 9.44-μm light, a luminous flux of 1 mW/μm2 can bring about a nonreciprocal temperature difference of 15 K, which endows the array with significant tunable absorption/emission capability, which is helpful for the development and application of future nonreciprocal thermal absorbing devices for the mid-infrared wavelength band.