<p>With the development of electronic components towards high frequency, high efficiency, and miniaturization, the demand for non-oriented silicon steel ultra-thin ribbons is increasing, which were usually prepared by multi-pass rolling with complex processes and high cost. The ultra-thin non-oriented silicon steel ribbons with silicon content of 2–4.5 wt.% Si were prepared with the planar flow casting technology, and the microstructure and properties of ribbons were investigated. The results showed that as the silicon content increased, the grain size of the as-cast ribbons gradually decreased, and the dislocation density and internal stress were higher. The proportion of {100} oriented grains gradually increased from 29.3 to 37.3%, and the ratio of {110} and {111} oriented grains decreased. Meanwhile, the magnetic induction <i>B</i>₅₀ showed a decline trend from 1.62 to 1.45&#xa0;T with the increase in silicon content, while the iron loss <i>P</i>_1.0/400 increased from 20.61 to 66.65 W/kg. This may be related to the silicon content affecting the wettability of melt and the wheel, thereby affecting the cooling capacity. The grains grew significantly after annealing, the internal stress was released and dislocations were eliminated. All this greatly improved the magnetic properties and decreased the hardness. <i>B</i>₅₀ of ribbons with 2 wt.% Si reached 1.66&#xa0;T and <i>P</i>_1.0/400 of ribbons with 4.5 wt.% Si was reduced to 13.40 W/kg. The percentage of {110} fiber grains increased obviously while {100} fiber grains decreased slightly after heat treatment.</p>