Abstract: The electromagnetic properties of 1.8%Si non-oriented silicon steel with different heating time were compared, the change rules of microstructure and inclusions were analyzed. The results show that the iron loss of the sample with long heating time in the hot rolling furnace was 0.43 W/kg, which was mainly because there were a large number of AlN inclusions with size less than 1 μm and irregular shape pinned at the grain boundary, which led to the failure of grain growth and the fine and uneven grain structure. A large amount of AlN was uniformly dissolved in the slab by heating furnace at 1 000~1 120 ℃ for a long time. In the process of rolling and cooling, AlN was precipitated in a dispersed and fine state and inherited into the cold coil. In the continuous heat treatment process of silicon steel unit, when the temperature reached above 950 ℃, AlN was precipitated in a dispersed and fine form after solid solution again. For the samples with normal heating time, even in the case of high temperature in the soaking section of the heating furnace, because AlN was not uniformly dissolved in each position of the slab, AlN was precipitated in a clustered state during rolling and cooling. The inclusions were mainly AlN, CaS-Al₂O₃, AlN-CaO-Al₂O₃ composite inclusions with relatively large size, and the electromagnetic properties were good.