In recent years, the function of Four-Dimensional(4D) trajectory prediction and optimization has become a hot research topic of Flight Management System (FMS) technology. The accuracy of track prediction results is directly related to the parameters of the aircraft, as well as the economy of the aircraft operation, and even determines the safety of the aircraft. From the point of view of aircraft operation cost, this paper establishes the cost function model of aircraft operation according to the operation cost, models the speed and altitude in the cruise phase respectively, optimizes the four-dimensional track prediction results with the cost function as the optimization object, and summarizes a set of calculation methods for the most economical cruise speed and the most economical cruise altitude. The paper provides a practical theoretical reference to optimize the four-dimensional track prediction for civil aircraft.