Traditional information retrieval systems have several shortcomings in common, such as delaying in information updating, costing additional host and network resources, and so on. The promise of mobile multi-agent technology is becoming highly attractive. We approach to apply the mobile multi-agent technology to information retrieval in order to build a brand-new system. Although the mobile multi-agent technology advantages information retrieval systems, it also brings several new negative problems. The most serious one is the security problem because of agent's mobility and initiative. In this paper, we firstly analyze the drawbacks of current information retrieval systems, and then describe how to employ the mobile multi-agent technology to the information retrieval system to improve its performance. What we discuss mainly in this paper is the security problems of the information retrieval system based on mobile multi-agent (IRSMMA). We analyze threats to the security of the new system, study out the security policies, and at last establish a robust and secure architecture name MMASA (Mobile Multi-Agent Security Architecture), which can effectively protect our system, and also adapt to other network application based on mobile multi-agent because of its generality.