Abstract: The vertical profile is an important way to show actual wellbore trajectory.It provides a projection curve of actual drilling trajectory on design plane.A general equation of projection calculation is derived from geometric theory. Common types of wellbore curves such as straight line,cy- lindrical helical and arc are analyzed in details,thus deriving a calculation equation for projection point.Calculation eases indicate that in the process of actual drilling,the vertical profile of 3D wellbore trajectory mapped by apparent projec- tion length can visibly compare the matching degree of actual drilling trajectory with the design trajectory,thus playing a good guide in wellbore trajectory prediction and controlling.