The present invention discloses a fastening system for a panel. The fastening system includes: at least two mounting rails which each has a plurality of engaging open cavities formed therein; and a plurality of engaging slide blocks respectively engaging with the engaging open cavities; wherein the panel is disposed on the mounting rails and fixedly connected with the engaging slide blocks respectively. Basing on the engagement structure, the present invention can be fastened on a surface of a mounted object via two rails and provide high tensile strength and simple installation. The present invention can fix different shapes of panel assemblies on a roof, the ground, a wall or a surface of a framework safely, quickly and stably, and the present invention has a simple structure, light weight and low total costs.