Abstract: The electromagnetic properties of a 50W1300 steel were deteriorated. The reasons for the deterioration of its electromagnetic properties were analyzed by means of chemical composition analysis, metallographic examination and texture analysis. The results show that when the Nb content in the steel was too high, a large number of fine and dispersed NbN, NbC and Nb (C,N) precipitated would appear. These precipitates pinned at grain boundaries, preventing normal grain growth, leading to fine grain clustering and the formation of island-like grains, ultimately deteriorating the iron loss value. Simultaneously, a large number of fine inclusions containing Nb element inhibited the formation of coarse and well-developed hot-rolled microstructures, promoting the weakening of the favorable texture—rotational cubic texture 100<011>, while the strengths of unfavorable textures 111<110> and 111<112> increased accordingly, adversely affecting the magnetic induction intensity. Finally, suggestions for precise control of Nb element content and optimization of hot-rolling process temperature were proposed, effectively improving the electromagnetic properties of 50W1300 steel.