An apparatus used for measuring a plant root system pullout force and a method thereof are disclosed and belong to the plant root system pulling force measurement technology field. The apparatus used for measuring the plant root system pullout force comprises a main frame, an assistant support, a swing arm, a clamping component, an air cylinder, an air pump, an air pressure sensor and a controller. One end of the main frame is provided with a first opening and one end of the main frame is movably installed on the assistant support. The swing arm is provided with multiple pairs of first shaft holes. The multiple pairs of first shaft holes are distributed at intervals along a length direction of the swing arm. A rotating shaft passes through one pair of first shaft holes on the swing arm and one pair of second shaft holes on the main frame so that the swing arm is installed in the main frame. The clamping component is installed on one end of the swing arm and the clamping component is provided with a second opening. The air cylinder is installed on the main frame. A piston rod of the air cylinder passes through the main frame and is connected to the other end of the swing arm. The air pump is installed on the main frame and is connected to the air cylinder through a gas guide tube. The air pressure sensor is connected to the air cylinder. The air pump and the air pressure sensor are connected to the controller.