The invention relates to a tensioning wheel used for maintaining constant tension by flexible transmission parts like a belt or a chain, in particular to a tensioning wheel with an asymmetrical damping mechanism, wherein the tensioning wheel with the asymmetrical damping mechanism can provide large frictional damping force in a loading process and can not provide frictional damping force or can only provide small frictional damping force in an unloading process. The tensioning wheel with the asymmetrical damping mechanism comprises a belt wheel, a swing arm and a base. The swing arm and the base are connected together through a spindle. The swing arm and the base are connected in a matching mode to form an enclosed cavity, and a bias component and the damping mechanism are arranged in the cavity. A plurality of convex-shaped supporting structures are arranged on the side face where the swing arm faces towards the base, the damping mechanism is composed of a damping piece and the supporting structures, and the supporting structures make contact with the bias component to be connected with the damping piece in a matching mode. The damping mechanism is used for generating frictional damping force to prevent belt fleeping caused by running of an engine.