Based on the framework and standards provided by HLA (High Level Architecture), simulation method of UCAV (Uninhabited Combat Air Vehicle) was studied. The federation structure of the simulation system was introduced. FOM (Federation Object Model)/SOM (Simulation Object Model) and time management of the federation are designed. Three ways such as real-time RTI end-system、communication assurance system and enforced predictable RTI service are adopted to meet the real time requirements. Factors that affect cruise height are also analyzed, and the models of the factors are established. According to the simulation procedure, federation simulation platform is designed by adopting MK RTI and Visual C++6.0. The results obtained from the simulation on the cruise height of UCAV are believable and detailed. The simulation system prepared the ground for the simulation of the UCAV combat tasks and can be a reference for the future development of the similar system.