The security technology decides the realization of the mobile agent. The primary problem solved by this paper is to prevent replay attacks and acts beyond its authorities of malicious mobile agent. The concepts, characters and security of mobile agent are described. Afterwards, the concepts and advantages of incremental timestamp are proposed, and a specific example and the demonstrations are also presented. The mobile agent system that adopts incremental timestamp can protect execute system from damages of hostile mobile agents.The incremental timestamp technology has been verified and realized in the mobile agent system which is developed based on the Lucent Company's Inferno system.