A hub motor for driving a wheel of an electric vehicle and includes a cylindrical casing fixed to the wheel of an electric vehicle and a ring gear and a coil unit are fixed to the casing. A central unit includes co-axial two fixed axles and a shaft. Multiple bearings are located between the casing and the central unit so that the casing is rotatable relative to the central unit. The shaft has a magnet unit and a sun gear fixed thereto, a planet gear frame is connected to the fixed axle by a one-way bearing. Multiple planet gears are connected to the planet gear frame. The planet gears are engaged with the ring gear and the sun gear. The hub motor is simplified structure and easily assembled.