A bone screw of minimally invasive fixation device for lumbar comprises a positioning casing (200) and a screw body (100). The positioning casing includes a rod securing base (210) and an alignment portion (220), which are integrally formed； an annular notch (230) is formed between them. The alignment portion has at least one pair of rod alignment openings (221, 222). Two longitudinal notches (224) extend from near the top across the alignment openings to the rod securing base. The screw body is rotatably connected to the bottom portion of the positioning casing； the spherical head of the screw body is arranged in a spherical pit of the rod securing base. The alignment portion 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.
