Abstract: This paper designs a UHF 6C tag with SPI interface to extend its application.The designed passive tag not only can be configured by MCU but also can access the external memory by SPI interface.In this paper,the working flow of tag under two modes which means the communication with MCU or external memory by SPI interface and the specific design of digital processor are analyzed in detail.The tag can carry external memory and can achieve high-capacity data storage capabilities.According to the function,baseband is realized by Verilog and the chip is fabricated with NEC13 process.The final area of baseband is only 515 μm×380 μm.