A cartridge for launching a bullet, includes a shell case, a pressure chamber and a push rod; the shell case defines concentric through-holes; the pressure chamber is set up between the through-holes; the push rod defines an air vent and an airway, the air vent being in fluid communication with the firing chamber via the airway; a piston is mounted to the push rod and is received in the pressure chamber for compressing the chamber; when uncompressed, the air vent is located in the pressure chamber, when the push rod is struck the air vent moves forwards, back into the pressure chamber, the compressed air in the pressure chamber is discharged via the air vent and the airway to fire the bullet. The invention has a simple and compact structure, and is safe in use.