Flight planning module includes the sub-functions such as flight plan management, flight path optimization calculation, and in-flight real-time implementation. Firstly, how to realize the artificial creation, automaticcreation, and state management of flight plans is discussed. Secondly, the realization of parallel tracks combination, three-dimensional trajectory optimization and four-dimensional track creation is studied. For the flight plan real-time implementation module, the realization of such functional modules as flight plan deviation, direct flight,holding, backup flight plan activation, en-route diversion, and circling holding is discussed, which are usually due to dangerous weather, ATC limitations, or aircraft configuration. Finally, the simulated calculation is done based on the data of B737-800 the results can provide a reference for the research of Flight Management System.