A bone screw of minimally invasive fixation device for lumbar, comprising a positioning casing, the positioning casing comprising a rod securing base, an alignment portion and an annular notch, wherein: the annular notch on the positioning casing is formed between the rod securing base and the alignment portion, the rod securing base and the alignment portion are integrally configured; the bottom of the rod securing base has a spherical pit and a through hole arranged on the bottom center portion of the spherical pit, the top of the alignment portion has a top opening and a passage is formed from the top opening of the alignment portion to the through hole of the rod securing base; the wall of the rod securing base has a pair of U-shaped openings aligned with each other such that a securing-base-passing passage laterally passing through the rod securing base is defined by the U-shaped openings 214; the wall of the alignment portion has at least one pair of alignment openings (221, 222) aligned with each other, and an alignment-portion-passing passage which allows an alignment fixture to laterally pass though the alignment portion is defined by at least one of the pairs of the alignment openings (221, 222); two longitudinal notches extend respectively on the wall of the alignment portion from adjacent to the top opening of the alignment portion; and the alignment portion of the positioning casing can be broken into two pieces and separated from the rod securing base by applying a force to the wall of the alignment portion to break the longitudinal notches as well as the annular notch so that the alignment portion can be removed from the positioning casing; characterized in that: the longitudinal notches extend downward across the alignment openings on each side to the U-shaped openings on each side. the positioning casing comprising a rod securing base, an alignment portion and an annular notch, wherein: the annular notch on the positioning casing is formed between the rod securing base and the alignment portion, the rod securing base and the alignment portion are integrally configured; the bottom of the rod securing base has a spherical pit and a through hole arranged on the bottom center portion of the spherical pit, the top of the alignment portion has a top opening and a passage is formed from the top opening of the alignment portion to the through hole of the rod securing base; the wall of the rod securing base has a pair of U-shaped openings aligned with each other such that a securing-base-passing passage laterally passing through the rod securing base is defined by the U-shaped openings 214; the wall of the alignment portion has at least one pair of alignment openings (221, 222) aligned with each other, and an alignment-portion-passing passage which allows an alignment fixture to laterally pass though the alignment portion is defined by at least one of the pairs of the alignment openings (221, 222); two longitudinal notches extend respectively on the wall of the alignment portion from adjacent to the top opening of the alignment portion; and the alignment portion of the positioning casing can be broken into two pieces and separated from the rod securing base by applying a force to the wall of the alignment portion to break the longitudinal notches as well as the annular notch so that the alignment portion can be removed from the positioning casing; characterized in that: the longitudinal notches extend downward across the alignment openings on each side to the U-shaped openings on each side. the annular notch on the positioning casing is formed between the rod securing base and the alignment portion, the rod securing base and the alignment portion are integrally configured; the bottom of the rod securing base has a spherical pit and a through hole arranged on the bottom center portion of the spherical pit, the top of the alignment portion has a top opening and a passage is formed from the top opening of the alignment portion to the through hole of the rod securing base; the wall of the rod securing base has a pair of U-shaped openings aligned with each other such that a securing-base-passing passage laterally passing through the rod securing base is defined by the U-shaped openings 214; the wall of the alignment portion has at least one pair of alignment openings (221, 222) aligned with each other, and an alignment-portion-passing passage which allows an alignment fixture to laterally pass though the alignment portion is defined by at least one of the pairs of the alignment openings (221, 222); two longitudinal notches extend respectively on the wall of the alignment portion from adjacent to the top opening of the alignment portion; and the alignment portion of the positioning casing can be broken into two pieces and separated from the rod securing base by applying a force to the wall of the alignment portion to break the longitudinal notches as well as the annular notch so that the alignment portion can be removed from the positioning casing; characterized in that: the longitudinal notches extend downward across the alignment openings on each side to the U-shaped openings on each side. the longitudinal notches extend downward across the alignment openings on each side to the U-shaped openings on each side.