This article proposes a new method for predicting the horizontal trajectory of flight plan segments, which belongs to the field of flight management system design. Unlike traditional methods that require calculating the turning center point first and then predicting the turning point based on the turning center point, this method analyzes the waypoint coordinates by converting them into three-dimensional coordinates. The specific steps include: (1) defining an ellipsoidal coordinate system, converting the longitude and latitude of position points into ellipsoidal coordinates; (2) Calculate the turning radius R, calculate the heading angle to be flown (positive for north latitude and east longitude input, negative for south latitude and west longitude input), and calculate the distance D from the starting point S of the turn to the middle waypoint; (3) Convert the waypoint and waypoint turning point to a spherical coordinate system, establish equations through coplanarity, and solve the turning point by combining it with the distance formula; (4) Smooth connect all turning points, complete horizontal trajectory prediction and generation, and output. The present invention converts the turning point and route into a spherical coordinate system, and calculates the longitude and latitude of the turning point by combining the three point coplanar and distance information equations to obtain the predicted route. This method has a clear idea, captures the core of the problem no problem.