The invention relates to sheet punching, in particular to a sheet punching device and a punching method of the sheet punching device. The sheet punching device comprises a cutter bar connected with a drilling machine, wherein the lower end of the cutter bar penetrates through a cutter frame bar, the cutter frame bar comprises a connecting arm and a fixing arm, the connecting arm penetrates through the lower end of the cutter bar in the radial direction and is fixed to the lower end of the cutter bar through a locking pillar, an included angle in the vertical plane is formed between the fixing arm and the connecting arm, and a blade is fixed to the lower end of the fixing arm. The sheet punching device has the advantages of being capable of adjusting machining sizes according to machining needs, not needing to replace cutters when machining holes of different sizes, saving machining time, being simple to operate, not needing secondary machining, being high in machining accuracy and the like.