The invention relates to compressor pistons and a mounting method and a fixture thereof. The end surfaces of piston seats of the compressor pistons are provided with positioning holes for mounting, the end surfaces of piston heads are planes without pits, the fixture for mounting the compressor pistons comprises a cylinder body base, a spindle holder, a round fixture and a plurality of positioning rods, wherein the spindle holder is positioned at one side of each cylinder body clamp, the round fixture is positioned between the cylinder body clamps and the spindle holder and is used for positioning the peripheries of the pistons, and the positioning rods are fitted in the positioning holes of the end surfaces of the piston seats. After a spindle, a swash plate and the pistons are assembled, the round fixture is moved to the outer surfaces of the pistons to radially position the pistons; the positioning rods are respectively inserted into the positioning holes of the end surfaces of the piston seats, the upper end of a spindle is held by the spindle holder, and the spindle is aligned with the central hole of a cylinder body; and the spindle holder and the positioning rods are moved downward to mount the piston heads into cylinder holes. The invention can reduce the displacement loss of the cylinder, and can accurately align the pistons with the cylinder in an automated assembly line.