A flat clamping hand tool structure includes a left clamping seat having one side with a left fixing portion facing a right fixing portion on one side of a right clamping seat. The first and second fixing members move up and down in left and right mounting slots of the left and right clamping seats by left and right swing plates which are pivotally connected with upper and lower holders. The left and right clamping seats are guided to move by guiding blocks of the upper and lower holders to slide along guiding grooves of the left and right clamping seats. Left and the right arms pivot together through a first pivot member. Left and right limit portions of the left and right swing plates mesh with each other so as to drive the left and right clamping seats to carry out a clamping motion.