A skull fixing device includes at least a lower fastening member and a movable retainer assembly. The lower fastening member includes a thread rod having a first coupling section formed in an interior thereof. The movable retainer assembly includes at least an upper fastening member and a nut. The upper fastening member includes a sleeve section in which a first rotation section is formed. The nut is screwed to the threaded rod and has an upper end forming a first positioning section and has an outer surface forming a second rotation section mating the first rotation section. Also disclosed is a surgery tool that includes at least a outer barrel having a lower end forming a second positioning section engageable with the first positioning section and an inner guide rod having a lower end forming a second coupling section engageable with the first coupling section.