A belt sander having a fast-lift cover structure includes a drive mechanism, a body and a cover. The drive mechanism includes a drive module, a tension arm, a sanding belt surrounding the drive module and the tension arm. The body receives the drive module. The body includes a base, an extendable support rod extended from the body and connected to the tension arm, and a cover fastening assembly disposed at the base. The cover fastening assembly includes a release and a resilient element for restoring the release to its original position. One end of a cover is pivotally connected at one side of the body, and the other end of the cover includes a fastening portion engaged with the release. Operation is easy, no hand tools are required, and the cover does not fall off.