A bone screw has a screw body with a spherical head and a screw rod and a positioning sleeve with a connecting rod fixing seat and a calibration part. An annular cutting slot is defined between the connecting rod fixing seat and the calibration part. At least two pairs of connecting rod calibration openings are formed on a sidewall of the calibration part. An axial cutting slot is formed on a sidewall of an adjacent region of the connecting rod calibration openings. The spherical head is connected to a top portion of the screw rod. The screw body is pivoted to a bottom portion of the positioning sleeve. The spherical head is sleevingly arranged on a spherical pit of the connecting rod fixing seat. The calibration part can be split into two pieces and separated from the connecting rod fixing seat. The calibration part is removable from the positioning sleeve.
