The present invention relates to a size-adjusting fastening mechanism for stakes comprising fixed locking grooves and a movable locking convex block, whereby when one of the grooves engages with the convex block, tooth position is loosened and toecap is telescopic upon pulling. When the groove and the convex block are rotated to deflect so as not to engage with each other, tooth position is pressed to lock so as to be irremovable. Such a structure requires that the pull handle be pulled horizontally forwards and backwards. Being secured with rivet punching, the claimed device possesses good stability, is simple in structure, low in cost and easy for operation.