The scarcity of materials with coexisting ferroelectric polarization and magnetization has hindered the development of multiferroic-based spintronic applications. Therefore, the generation of polarization in magnetic compounds is an important task in an effort to make single-phase multiferroic materials. Magnetic domain walls with strong discontinuities in spin ordering provide an ideal platform for the generation of polarization. In this work, we investigate spin-induced ferroelectric polarization at antiferromagnetic domain walls in the rare-earth orthoferrites AFeO3 (A = Lu, Y, Gd). We find that the ferroelectric polarization depends on the atomic radius of the rare-earth element, with the largest polarization of 0.092 μC cm-2 being realized in LuFeO3, which has the smallest rare-earth radius and the highest domain wall density along the b direction. Based on the octahedral distortion and the unified polarization model, we also perform a mechanistic analysis of the ferroelectric polarization at domain walls along the b direction. The different octahedral tilt angles and the different unit cell volumes caused by A-site ions are the main reasons for the polarization difference in the three compounds. Our results improve the theoretical understanding of magnetically induced ferroelectric polarization at domain walls and provide a basis for experimental application in spintronic devices based on domain wall multiferroicity.