A bone screw of minimally invasive fixation device for lumbar comprises a positioning casing and a screw body. The positioning casing includes a rod securing base and an alignment portion, both of which are integrally formed; an annular notch is formed between them. The alignment portion has at least two pairs of rod alignment openings in a bulb-shaped or keyhole-shaped form with an upper portion larger than a lower portion. Two longitudinal notches extend from near the top across the alignment openings to the rod securing base. The screw body includes a spherical head and a screw rod; the outer diameter of the spherical head is larger than that of the screw rod. The screw body is rotatably connected to the bottom portion of the positioning casing; the spherical head of the screw body is arranged in the spherical pit of the rod securing base.