A circular stapler comprising a knob assembly, wherein, a screw rod is provided in the stapler, the knob assembly comprises: a knob driver capable of being rotated by an external force; a knob body sheathed outside the screw rod , wherein when the knob body rotates, the screw rod is driven to move along an axial direction of the stapler to drive an anvil assembly towards an cartridge assembly of the stapler; a first cooperating component having a blocking state and an unblocking state, wherein the first cooperating component is an elastic sheet having two ends and a protruding portion between the two ends ; a second cooperating component; wherein when the first cooperating component is in the blocking state, the first cooperating component and the second cooperating component are fixedly linked with each other, when a rotating resistance to the knob body is larger than a preset resistance value, the elastic sheet is deformed by a force of the second cooperating component and enters the unblocking state, then the first cooperating component and the second cooperating component are not fixedly linked with each other; wherein the first cooperating component is provided at the knob driver, and the second cooperating component is provided at the knob body , and the knob driver is provided with mounting grooves for the two ends of the elastic sheet ; or the first cooperating component is provided at the knob body , and the second cooperating component is provided at the knob driver, and the knob body is provided with mounting grooves for the two ends of the elastic sheet ; wherein the two ends of the elastic sheet are correspondingly mounted in the mounting grooves . a knob driver capable of being rotated by an external force; a knob body sheathed outside the screw rod , wherein when the knob body rotates, the screw rod is driven to move along an axial direction of the stapler to drive an anvil assembly towards an cartridge assembly of the stapler; a first cooperating component having a blocking state and an unblocking state, wherein the first cooperating component is an elastic sheet having two ends and a protruding portion between the two ends ; a second cooperating component; wherein when the first cooperating component is in the blocking state, the first cooperating component and the second cooperating component are fixedly linked with each other, when a rotating resistance to the knob body is larger than a preset resistance value, the elastic sheet is deformed by a force of the second cooperating component and enters the unblocking state, then the first cooperating component and the second cooperating component are not fixedly linked with each other; wherein the first cooperating component is provided at the knob driver, and the second cooperating component is provided at the knob body , and the knob driver is provided with mounting grooves for the two ends of the elastic sheet ; or the first cooperating component is provided at the knob body , and the second cooperating component is provided at the knob driver, and the knob body is provided with mounting grooves for the two ends of the elastic sheet ; wherein the two ends of the elastic sheet are correspondingly mounted in the mounting grooves . <EOS>