A JTAG circuit with a protection module comprises a TAP controller, an instruction register, an instruction encoder, the protection module, a BYPASS register, a device ID register, a boundary scanning register, a TDO circuit, an input port and an output port, and is characterized in that a locking instruction and an unlocking instruction are added on the basis of the IEEE 1149.1 standard; the locking and unlocking of the JTAG circuit are controlled in a code identification manner to prevent an illegal user from controlling the JTAG circuit, effectively improve the safety of the JTAG circuit, and prevent the outside to attack a chip system through the JTAG circuit. The JTAG circuit can be completely compatible with the IEEE 1149.1 standard, and is low in hardware cost.