Abstract: For the security of data stored in the mobile hard disk,the AES algorithm is optimized and a pipelined encryption and decryption system which combines a Microblaze with an AES core is presented.The security card is designed to work between the USB interfaces of the computer and the mobile hard disk.A traditional mobile hard disk can be turned to a security one simply by using this card.The experimental results on Spartan6-Nexys3FPGA show that the encryption and decryption system can achieve 174.08Mb/s at 120MHz clock with very low resource consumption.