We discuss design and implementation of a script language for an AMS (Automated Manufacturing System) simulator. The script language is used for detailed modeling of the operating rules in the simulator. We discuss design and development of a script interpreter and executor for the simulator. The script interpreter generates an intermediate representation from a script input file and the script executor performs the operations specified in the intermediate representation. We propose the use of an MDD (Multiple-valued Decision Diagram) as a data structure of the intermediate representation in addition to a tree structure that is generally used in the interpreters. The MDD structure reduces the memory requirement and execution time when we implement the script for the operating rules of a state enumerated controller that specifies the control action for each state of the system. We present some modeling examples.