A winding device with a planetary-roller tear-off mechanism is disclosed, comprising a first winding roller which is driven to rotate in a predetermined direction and a plurality of core support plates that are arranged at a predetermined distance below the first winding roller, wherein an interval between the core support plates and the first winding roller is defined as a curved channel. A web material is conveyed through the curved channel to a winding zone to be wound as a roll. The planetary-roller tear-off mechanism includes a plurality of rotary arms and a plurality of planetary rollers. Each rotary arm is set at a predetermined location below the first winding roller, and having a driving end and a free end. Each planetary roller is rotatable, and mounted to the free end of the respective rotary arm. When the free end of the rotary arm is driven to rotate to a position facing a circumferential surface of the first winding roller, the web material is subjected to a drag force acting thereon to break the web material.