A circular stapler with an automatic safety function, comprising - a stapler body, - a stapler head, - an actuating mechanism and - a transmission adjusting mechanism; wherein the actuating mechanism comprises a handle and a handle coat, the handle is connected with the handle coat and is pivotally connected with the stapler body, the transmission adjusting mechanism comprises a screw rod and an adjusting knob, the front end of the screw rod is connected with an anvil pulling rod while its rear end is connected with the adjusting knob by means of screw threads, characterized by further including: - a stopper disposed either inside said handle or said handle coat; - a safety rod having a safety block on one end, a protruding block B and a pin hole as its middle portion; a cylindrical pin is inserted into the pin hole to pivotally connect the safety rod with the stapler body, wherein the safety block is rotatable on the cylindrical pin between a non actuatable position, in which the safety block props against the stopper so that the handle cannot be gripped, and an actuatable position, in which the safety block is completely disengaged from the stopper so that the handle can be gripped; - a pulling sheet having a rear portion mounted on the screw rod and a front portion divided into three plates extending in the longitudinal direction of the pulling sheet, said three plates including a middle plate between two side plates (11a, 11b), the middle plate including a pulling hook at its front portion, the pulling hook protrudes from the side plates and hooks with the protruding block B of the safety rod from said non actuatable position to said actuatable position, wherein a rotation of the adjusting knob moves backwards the screw rod and the screw rod drives the pulling hook to move backwards to rotate clockwise the safety rod in said actuatable position; -; a protruding -block A is disposed on the handle; and when the handle is gripped, the protruding block A props against and pushes away said middle plate, thereby the pulling hook is disengaged from said protruding block B; - a restoring spring is provided so as to connect the safety rod with the stapler body and to reset the safety block in the non actuatable position when the handle is released, the restoring spring rotating the safety block anticlockwise around the cylindrical pin, until the safety block props against the stopper to automatic prevent a second actuation of the circular stapler. - a stapler body, - a stapler head, - an actuating mechanism and - a transmission adjusting mechanism; wherein - a stopper disposed either inside said handle or said handle coat; - a safety rod having a safety block on one end, a protruding block B and a pin hole as its middle portion; a cylindrical pin is inserted into the pin hole to pivotally connect the safety rod with the stapler body, wherein the safety block is rotatable on the cylindrical pin between a non actuatable position, in which the safety block props against the stopper so that the handle cannot be gripped, and an actuatable position, in which the safety block is completely disengaged from the stopper so that the handle can be gripped; - a pulling sheet having a rear portion mounted on the screw rod and a front portion divided into three plates extending in the longitudinal direction of the pulling sheet, said three plates including a middle plate between two side plates (11a, 11b), the middle plate including a pulling hook at its front portion, the pulling hook protrudes from the side plates and hooks with the protruding block B of the safety rod from said non actuatable position to said actuatable position, wherein a rotation of the adjusting knob moves backwards the screw rod and the screw rod drives the pulling hook to move backwards to rotate clockwise the safety rod in said actuatable position; -; a protruding -block A is disposed on the handle; and when the handle is gripped, the protruding block A props against and pushes away said middle plate, thereby the pulling hook is disengaged from said protruding block B; - a restoring spring is provided so as to connect the safety rod with the stapler body and to reset the safety block in the non actuatable position when the handle is released, the restoring spring rotating the safety block anticlockwise around the cylindrical pin, until the safety block props against the stopper to automatic prevent a second actuation of the circular stapler.