In order to meet the needs of studying the actual flight route of vertical navigation, the dynamic equation of the climb process was established, and the calculation method of the VNAV departure performance parameters was constructed. And taking the data of a certain domestic civil aircraft model as an example, the differences between VNAV climb and traditional climb were compared and analyzed. The research has shown that in the process of vertical navigation climb, because the required thrust is less than the maximum climb thrust, the time required for the aircraft to reach the target altitude, the horizontal distance of the climbing, and the fuel consumption are greater than those of conventional climbs; when the climb angle/rate of climb increases to a certain value, the required thrust is limited by the maximum climb thrust, which is equivalent to a conventional climb. In the research of flight plan preparation and departure trajectory optimization, it is necessary to consider the difference between VNAV climb and traditional climb to improve the accuracy and effectiveness of prediction.