PM_2.5 emissions from iron and steel and nonferrous industries as object, based on the discrete particle model DPM and UDF custom programming, The effects of inlet velocity, particle diameter, external magnetic field strength, magnetic fiber magnetic flux density and magnetic susceptibility on the capture efficiency were studied and analyzed by combination between the particle motion trajectory and force. The results showed that when 0.5μm£d_p£2.5μm, v=0.1m/s, the efficiency of single fiber to capture PM_2.5 could be improved by using high gradient magnetic field(H=0.1T, B=0.06T)4.23times. It was also found that there were two gravitational zones and two repulsive zones around the magnetic fibers. At the same time, in the high gradient magnetic field, the capture efficiency of the magnetic fiber to PM_2.5 decreased first and then stabilized with the inlet velocity; while the capture efficiency increased first and then decreased with the particle diameter of the dust. When d_p=1.0μm, the increasing of capture efficiency was maximized at this time; whether it was the external magnetic field strength or the magnetic fiber magnetic flux density, the capturing efficiency of magnetic fiber to particles was a linear function of the field intensity, with the efficiency growth rate of K_B>K_H; with the increase of the magnetic susceptibility of the particles, the capturing of particles by magnetic fibers presented a two-stage linear growth law, and the growth rate K₁>K₂. When the particles passed through the high gradient magnetic field, the inlet velocity, dust particle diameter and field strength had a great influence on the motion trajectory, while the magnetic susceptibility had little effect on the motion trajectory.