Abstract: Nonreciprocal thermal radiation is a novel approach to radiative heat transfer that breaks through the symmetric reciprocity of traditional Kirchhoff's law. It overcomes the restriction that the spectrally oriented emissivity and spectrally oriented absorptivity of an object must be equal, allowing independent control of the spectral and angular emissivity and absorptivity of a radiator in both time and space. This paper reviews the progress of research on nonreciprocal thermal radiation in theoretical calculations, experimental verifications, and applications. Starting from the intrinsic connection between Kirchhoff's law and Lorentz reciprocity, it elaborates on the necessary conditions for the generation of nonreciprocal thermal radiation. Using two typical materials, magneto-optical materialsof InAs and Weyl semimetal, as examples, the paper explores how to construct asymmetric structures and utilize external field modulation to generate multi-wavelength and multi-angle nonreciprocal thermal radiation. These advancements have been applied in many fields, such as solar cells and thermophotovoltaic systems, successfully surpassing the blackbody limit of thermal radiation and theoretically reaching the Landsberg limit, thereby improving energy conversion efficiency. In the future, nonreciprocal thermal radiation is expected to provide strong support for efficient energy utilization and emission reduction, promote cutting-edge materials research and technological innovation, and inject new impetus and vitality into sustainable development.