The invention discloses a prepunching device of a firework tube assembling machine. The prepunching device comprises an up-down moving plate, hole insertion needle bases, up-down adjusting plates, sliding assemblies, fixing plates, stroke cylinders and hole insertion cylinders. The hole insertion needle bases are mounted on the up-down moving plate and are each provided with a hole insertion needle. The two ends of the up-down moving plate are mounted on the up-down adjusting plates. The sliding assemblies are provided with sliding grooves. Sliding blocks are arranged in the sliding grooves. One end of each sliding block is connected with the corresponding stroke cylinder. The other end of each sliding block is connected with the corresponding up-down adjusting plate. The stroke cylinders drive the sliding blocks to make the up-down moving plate move transversely. The sliding assemblies are connected with the hole insertion cylinders. The hole insertion cylinders are fixed to the fixing plates. The hole insertion cylinders drive the sliding assemblies to drive the up-down moving plate to move up and down. The prepunching device is novel in structure and good in safety, the insertion lengths of leads are consistent, and operation is convenient.