As the surroundings of airports will have great effect on approach landing systems' guidance parameters, the increasing air traffic and the new buildings on most of the modern airports are of serious threat to the operation of navaid and landing system. So it is necessary to perform a theoretical analysis and a numerical simulation before every major construction activity on the airport or approach landing system's installation. In this paper, the numerical system simulations (NSS) for approach landing systems are discussed, including the purpose, the methods applied, the process flow of system simulations, and the frame of software system of NSS. Simultaneously an example is given.