Mobile Software Agent (MSA) is a new distributed computing model that can meet the needs of current computing environment. In MSA model, computing tasks are encapsulated into agents and are implemented through agent migration and interaction. Because MSA is still in research phase presently, there are still no explicit definition to MSA model and appropriate solutions to some implementation technical problems of MSA system. In addition, the application domains for MSA are still under exploration. In this paper, we present a general purpose mobile software agent system, called JMSAS. Firstly, we define explicitly the MSA Model. Secondly, we introduce the architecture of JMSAS system, agent running manner and key technology in agent migration and agent communication implementation. Finally, we propose some ideas of the workflow management based on MSA.