Disclosed are a method and a structure for cutting off web in a winding machine. The winding machine includes an upper winding roller having a circumferential surface close to and below which a cut-off mechanism is arranged. The cut-off mechanism includes a pivot shaft having an outer circumferential surface and at least one pinch arm having a connecting end mounted to the outer circumferential surface of the pivot shaft and a web engagement end extending outward from the outer circumferential surface of the pivot shaft and forming at least one suction opening. At least one cutting blade is provided on the web engagement end of the pinch arm at a location immediately by the suction opening. When the pinch arm is driven to rotate the web engagement end to an engagement position where the web engagement end opposes the upper winding roller, the suction opening of the web engagement end sucks and holds a web material passing therethrough, whereby the web material is subjected to a pulling force induced by a roll of paper formed in a winding nip and is thus stretched to have the cutting blade set in tight engagement with the web material to cut off the web material.