The invention discloses a fixed clamping device for a geogrid and a working method thereof. The fixed clamping device for the geogrid comprises a shell, a fixing assembly and clamping assemblies, wherein a support bottom plate is fixedly arranged at the bottom end of the shell; four support foot brackets are fixedly arranged on the bottom surface of the support bottom plate; lifting air cylindersare fixedly arranged on the upper surfaces of the support foot brackets; square-shaped lifting rings are fixedly connected to the output ends of the lifting air cylinders and sleeve the outer side ofthe shell; connecting rods are fixedly connected to the front surfaces and the right surfaces of the square-shaped lifting rings; and the clamping assemblies are fixedly connected to one ends of the connecting rods. According to the fixed clamping device for the geogrid and the working method thereof provided by the invention, a drive motor runs, and the internal parts are interacted to drive a fixed drill bit to insert into the ground, so that the device remains stationary; and a rotary top cover is twisted to enable a second threaded rod to rotate, the clamping assemblies clamp the geogrid,and the geogrid remains stationary during welding, so that the welding effect of the geogrid is improved, and the engineering quality is ensured.