Mobile code computation has lead to a new paradigm of distributed computation. A mobile process can move from site to site and interact with the resources as a local process. To prevent the misuse resources, authentication and authorization need to be dealt with. Many modeling languages have been proposed to model distributed computation; Ambient Calculus [1] is one of them. Ambient Calculus, a type of process calculus, can be used to model boundary crossing activities in a mathematical notation. SJAN, a modeling language, extends the basic idea of Ambient Calculus, but it has a simple notation, design and representation. SJAN can be verified by J-Ambient, a JAVA implementation, to certify the correctness of the model. In this paper, we will introduce SJAN notation and J-Ambient. SJAN can be also used to model grid computation and provides the security consideration. Thus, finally, we will address several security scenarios in SJAN to show its functionality.