The invention relates to a flywheel type arc-shaped rotary cutter in rotational symmetry used for cultivating land roughly and weeding. The blades of the flywheel type arc-shaped rotary cutter in rotational symmetry take the shape of a circular arc; a raised fly wheel is arranged on the side surface and connected with the cutter surface through welding; the blade of the cutter is sharp; and the included angle a between two adjacent blades ranges from 30 to 70 degrees. Through the adoption of the structure, the sharpness and the work efficiency of the rotary cutter are improved, the resistance force of grass roots and soil to the rotary cutter and the force of friction of the tool nose are also reduced; and in addition, the blade temperature is not easy to increase, and vibration is not possible to occur during rough cultivating, so that the service life of the rotary cutter can be prolonged. As the flywheel type arc-shaped rotary cutter is formed through extrusion (or forging), the thickness is uniform, and cutter jumping phenomenon during rotary cultivating is avoided, and the stability in rotation of the flywheel type arc-shaped rotary cutter in rotational symmetry is ensured. In this way, the impact influence on a motor caused by various unstable loads is eliminated, and the stability in work of the motor is guaranteed.