In order to achieve ultra-low emissions of fine particles in the steel industry, magnetic fibers are proposed to improve the trapping efficiency of Fe-based fine particles. Based on CFD-DPM (Discrete Phase Model), the effect of traditional fiber and magnetic fiber diameter on the trapping efficiency of Fe-based fine particles and the filtration resistance of the fiber was studied. The results showed that there was no obvious difference in filtration resistance between magnetic fiber and traditional fiber. When the wind speed was 0.10 m/s, for fibers with a diameter in the range of 35~45 μm, the increase in diameter can significantly increase the filtration resistance. Traditional fibers had a low trapping efficiency for particles with a particle size of less than 2.5 μm. As the particle size increase, the trapping efficiency gradually increased. When the wind speed was in the range of 0.01~0.10 m/s, as the wind speed increased, the traditional fiber trapping efficiency decreased first and then increased. For the trapping efficiency of particles with a particle size of 4.5 μm, the traditional fiber diameter had an optimal range of 15~25 μm. For particles with a particle size of less than 2.5 μm, the increase in the diameter of the magnetic fiber had a relatively small effect on the improvement of the trapping efficiency. When the particle size was greater than 2.5 μm, increasing the fiber diameter can significantly improve the trapping efficiency. When the wind speed was in the range of 0.01~0.05 m/s, increasing the fiber diameter had a significant effect on improving the magnetic fiber trapping efficiency; when the wind speed was 0.08~0.10 m/s, the effect of the change in fiber diameter on the trapping efficiency was smaller. The quality factor of magnetic fiber decreased with the increase of fiber diameter. When the fiber diameter was in the range of 10~35 μm, the decreasing rate of the quality factor of increasing fiber diameter was small, and when the fiber diameter was in the range of 35~45 μm, the decreasing rate of quality factor was larger.