The invention discloses a seat gear shaft, and belongs to the field of gear shafts. The seat gear shaft comprises a shaft body and a gear, wherein key grooves are both formed in the upper side face and the lower side face of one end of the shaft body, sliding blocks are both fixedly connected to the upper side face and the lower side face of the inner end of the gear, the sliding blocks are slidably connected to the interiors of the key grooves, arc-shaped grooves are formed in the side faces of one ends of the key grooves, the sliding blocks are slidably connected to the interiors of the arc-shaped grooves, and the side surfaces of the end parts of the arc-shaped grooves are fixedly connected with clamping blocks; clamping grooves are formed in the side surfaces of the sliding blocks, theclamping blocks are clamped into the interiors of the clamping grooves in a clamped mode, first welding grooves are both formed in the side surfaces of the two ends of the gears, second welding grooves are both formed in the side surface of the shaft body, the first welding grooves correspond to the second welding grooves, the surface of the gear is fixedly connected with a glass fiber layer, thethickness of the gear is 1-2 cm, an epoxy resin layer is coated with the surface of the glass fiber layer, and the thickness is 1-2 mm. According to the seat gear shaft, the welding area of the gearand the shaft body can be increased through the first welding grooves and the second welding grooves, and the welding effect is improved.