Abstract: A method for data security transmission based on IPv6/IPv4 tunnel was designed and put into practice. On the basis of the analysis of IPv6 tunnel and security technique, and the adoption of manual tunnel and MD5 & RSA encryption algorithm to encrypt and encapsulate transmission data, the data security transmission of instant message and FTP in IPv4 network environment was realized on Windows XP SP2 operating system with C#.NET language used.

Key words: IPv6, manual tunnel, data security, data transfer, Internet