Abstract: The security of the third generation mobile system is built on the security of the second generation mobile system, by adopting the secure that have been proved essential and strengthened of the GSM generation mobile system, and rectifying the disadvantage of the second generation mobile system. This paper is devoted to the security of 3G mobile communication system. It firstly introduces the security requirements security architecture of 3G and the security menaces faced. Then mainly discusses security strategy of 3G.It is of great significance for Chinese 3G system construction in the near future.