In this study, a magnetic field perpendicular to the electric field is introduced to the gear-cylinder dielectric barrier discharge (DBD) to enhance the plasma density and improve the volatile organic compounds removal performance at atmospheric pressure. Higher discharge intensity, enlarged plasma streamers region, and better toluene removal performance are obtained after introducing a 0.2 T magnetic field due to the intensified ionization reactions caused by the Larmor movement of electrons. Time-resolved Intensified Charge-coupled Detector images indicate that both the propagation velocities of the primary and secondary streamers are enhanced and their durations are prolonged by the magnetic field. The optical emission spectra results imply that the vibrational temperature (Tvib) of N2(C-B) and the reduced electric field (E/N) are promoted by applying the magnetic field, while the rotational temperature (Trot) of N2(C-B) is rarely affected by the magnetic field. There is an optimal combination between the electric field and magnetic field in the gear-cylinder DBD reactor, according to the mechanism of the magnetically assisted DBD plasma. The pulsed discharge current, toluene removal efficiency, and energy yield with the magnetic field are increased by 26%–40%, 50%–70%, and 7%–20% within the range of 16–20 kV, respectively, compared to those without the magnetic field, implying that magnetically assisted DBD plasma presents superior toluene degradation performance compared to common DBD plasma.