Abstarct: With the growth of industry and human knowledge, the invention of the gearbox and its use for power transmission, torque, speed conversion, and rotation change in various types of industrial machinery, spread. Mechanical gearboxes are the most widely used in the industry due to their high torque and efficiency. Contact communication between the gears in the mechanical gearbox requires high maintenance and therefore high operating costs. This problem does not exist in magnetic gearboxes due to their non-contact torque transmission characteristics. In general, magnetic gearboxes are divided into two types, passive and active. Passive gearboxes usually have a fixed gear ratio, but in active magnetic gearboxes, the gear ratio can be varied over a wider range. Meanwhile, coaxial magnetic gearboxes of both active and passive types attract more attention due to their high torque density and wider application. For this purpose, in this dissertation, first, the finite element analysis of passive coaxial magnetic gearbox was performed in JMAG-Designer software to examine the changes in losses and load torque with respect to speed changes. Finally, a new structure of the active magnetic gearbox was proposed to reduce losses and improve the torque level in the passive gearbox. The analysis of this structure by the finite element method, which was accompanied by changes in the components of the intermediate modulator ring, showed that the efficiency of the proposed structure is significantly improved at high speeds. It is also possible to control the load angle and change the gear ratio in the proposed gearbox.