Abstract: The SD (Secure Digital) Memory Card interface defines two alternative communication protocols:SD and SPI.Based on analyzing SD card transport protocols,a design scheme of SD mode slave interface is proposed in this paper.The design can decode and response to host commands automatically,Flash can be read and written when connected with Flash controller.FIFO (First-In First-Out) is used in order to solve timing problem.FPGA (Field Programmable Gate Array)-based prototyping testified it can be recognized by computer as a SD card and satisfied the design goal completely.