Compared with outdoor electro-optical countermeasure test, indoor test has the advantages of flexibility, controllability and low-cost and can overcome some constraints of the outdoor test. According to those advantages of the indoor test, an idea for building an electro-optical countermeasure simulation system is proposed. Firstly, the main functions and components of the software platform for the electro-optical countermeasure simulation system are presented. Then, the design and application of the software platform are illustrated in detail. This software platform is successfully used in a distributed electro-optical countermeasure test system. It is also helpful to the building of similar systems.