An ink-staining anti-theft cash box includes a cash box mounted in a host machine for receiving and storing bills, an ink-jet module and an anti-theft security device consisting of a gas cylinder, a needle valve unit, a drive unit and a trigger unit. When the trigger unit detects abnormal separation of the cash box from the host machine, the trigger unit is triggered, and the drive unit is activated to move the gas cylinder toward the needle valve unit from a first position to a second position where an air seal diaphragm of the gas cylinder is pierced by the needle valve unit, and the compressed gas of the gas cylinder is released through an ink tub into an ink cartridge to force an ink out of a nozzle assembly of the ink-jet module for staining storage bills in the box body, enhancing the security level of the cash box.