The invention discloses a grinding device for cold-formed section steel and a working method of the grinding device. The grinding device comprises sliding seats, a first transverse sliding rod, a first adjusting motor, a second transverse sliding rod, a first screw, an upper transverse supporting rod, a lower transverse supporting rod, a second adjusting motor and a second screw, wherein the second adjusting motor is assembled at the outer side of one fixed plate and located at the upper end of a base, the output end of the second adjusting motor is connected with the second screw, vertical strips are mounted on one side face of a vertical plate, a sliding block is mounted on each vertical strip in a sliding mode, a mounting plate is mounted on the side face, away from the corresponding vertical strip, of each sliding block, a driven screw is mounted between an upper top plate and a lower bottom plate, an adjusting nut block is mounted on the annular side face of the driven screw in athreaded engagement mode, each sliding seat is mounted on the annular side face of a longitudinal rod in a sliding mode, and a moving transverse rod is mounted between an inner connecting seat and anouter connecting seat. According to the grinding device, manual handheld grinding of the cold-formed section steel is replaced, grinding facilitates adjustment in all directions, and the adjustment isconvenient, fast and stable.