Abstract: To improve the electromagnetic torque of disc-type micromotor, the effects of torque characteristics, magnetic field distribution, and thermal convection on air-gap flux density and armature current intensity were investigated. According to the Ampere’s law, the electromagnetic torque formula for the plane electronic winding in the axial flux of magnetic field was derived. Three-dimensional（3D） numerical calculation and actual measurement were carried out on the air-gap magnetic field produced by the permanent magnets, and the most important factor for increasing the magnetic flux density was found out. According to the air convection heat transfer mechanism based on thermal-fluid coupling, the temperature field distribution law was analyzed and measured, and an active cooling structure being conductive to convection was proposed. The study results show that the air-gap thickness has a significant effect on magnetic flux density, the torque constant increases 22.6% when the air-gap thickness decreases from 1.5mm to 1.0mm, while the magnet thickness has a saturation characteristic. Establishing the convection channel helps dissipation of Joule heat, and increases the current intensity by 52%. The designed micromotor owns good performance and high practical value. The proposed calculating and analyzing method has a high precision and the potential for popularization.