The instant disclosure relates to a flat heat pipe structure, which includes a flat tubing and a support member. The flat tubing has two opposed main walls and two opposed connecting walls connected thereto. The main and connecting walls cooperatively define an internal space. The inner surfaces of the flat tubing are covered with a capillary structure. The support member is disposed in the internal space of the flat tubing and has at least one support arm. The support arm extends in the longitudinal direction of the flat tubing. The support arm has two opposed surfaces abutting to the capillary structure of the main walls.