A Joint Test Action Group (JTAG) apparatus and a method for implementing JTAG data transmission are disclosed. The JTAG apparatus includes an isolation circuit connected with a processor and pins of a JTAG programmable logic device, wherein the isolation circuit has a register/registers corresponding to the pins of the JTAG programmable logic device. Based on a high or low level signal written into the register/registers of the isolation circuit by the processor, the isolation circuit drives the pins of the JTAG programmable logic device, and transmits the JTAG data corresponding to the high or low level signal from the processor to the JTAG programmable logic device. The isolation circuit is used to implement protection of a JTAG interface or a serial port of a personal computer connected with the JTAG apparatus.