An expandable fixing device contains: a first screw and a second screw. The first screw includes a first head portion and a first extension extending downwardly from the first head portion, the first extension has first threads formed on the first head portion, the first screw further includes a screwing orifice defined in the first head portion and multiple slots formed on the first extension, and the first extension has multiple expansion portions formed on a distal end thereof and intersecting with the multiple slots. The second screw includes a second head portion and a second extension extending downwardly from the second head portion, and the second extension has second threads formed on an outer wall thereof, wherein the second extension has a strike stem and inserting into the screwing orifice via the first screw and pushes the multiple expansion portions to expand outwardly.