The advanced encryption standard is the mainstream encryption algorithm in the security network protocol used in Linux system. Through analysis of AES encryption algorithm,with the architecture characteristics of the Loongson platform,the method for performance optimization of AES based on the expansion of multimedia instructions (SIMD technology) is proposed. Before and after optimization,the results of data transmission using security file transfer protocol Sftp (AES encryption) shows that the Loongson SIMD optimization has reduced the time of encryption and decryption and has effectively improved the Sftp network transmission rate.