The invention discloses tax control equipment based on a COS system, and belongs to the information safety field. The tax control equipment based on a COS system is characterized in that: a communication management module is responsible for data communication between a COS system layer for tax control and an interface layer; a command analysis module is used for making grammar analysis for the received command, and calling the corresponding function module according to the meaning of command parameters; a state machine module includes a tax control state machine and a PKI (Public Key Infrastructure) state machine; a file management module includes a tax control file system and a PKI file system; the tax control state machine is corresponding to the tax control file system; the PKI state machine is corresponding to the PKI file system; and the command analysis module distinguishes the tax control state machine, the tax control file system, the PKI state machine and the PKI file system according to the CLA field, and performs conversion of the corresponding state machine and operation of the corresponding file system. The tax control equipment based on a COS system can realize that the tax control business and the PKI business are not influenced mutually and the data are not crossed through an effective mode, and at the same time the COS system for tax control can be shared.