Abstract: This paper presents a mobile agent system security mechanism for large scale network applications. In this mechanism, we use a bidirectional authentication technology based on mixed encryption to resolve the mobile agent system local security problem. Mobile Agent Security Management Platforms (MASMP) working on different levels is applied to deal with the key distribution and management and control the emigration and task attribution of mobile agents. In order to resolve the problem of mobile agent security transference from one network to another, a task transfer model based on the credibility between two conjoint level MASMPs is designed. All these plans together resolve the mobile agent system security problem well. Because of its hiberarchy system structure and management model, this mechanism is very suit for large scale network applications.