This article is with the background of speech coding and data encryption, design a project of speech secure communication based on the TMS320VC5509A DSP. In system, the algorithm of MELP is adopted to encode voice data, AES algorithm is used to encrypt the speech signal data, and Differ-Hellman agreement is adopted as the key consultation. Because the adoption DSP realization and software module design, the system has to expand goodly, can replace the speech compression to code algorithm and encrypt algorithm, so the system can be the low bit rate speech again the solid hour keeps secret the experiment terrace of the communication. Finally, the system through the test very well, and realize basically the design request.