A high fidelity, reliable and extensible real-time CDU simulation system is built on the basis of self-made membrane keyboard and object-oriented simulation method in this paper to improve the visual feelings and simulation fidelity of CDU in flight management system research. Based on embedded PC104 CPU and 8255 programmable peripheral equipment interface card, the membrane keyboard hardware circuit and the keyboard code scanning program are designed. Accordingly, the confused logical problem of keystokes is solved and meanwhile, the emulation CDU keyboard is realized. And then, an extensible and reliable CDU pages system is constructed utilizing object-oriented simulation technique, inheritance and polymorphism mechanisms. Thus, the tiresome generation and management problem of pages system is tackled. Simulation experiments illustrate that routing data and performance parameters can be input and displayed realistically on the CDU system developed in this paper.