Climbing performance is one of the most critical indicators for evaluating aircraft flight performance and affecting flight safety. In the paper, the airworthiness regulations related to climbing performance in CCAR25 are researched and summarized in detail. An exhaustive method for calculating climb gradient during constant airspeed climb is developed. Meanwhile, the forward and reverse heading sawtooth climb method is designed to execute the climbing performance flight test. Finally, by comparing the calculation results of the climb gradient with the flight test results, it is proved that the aircraft meets the airworthiness requirements and the climb performance calculation model is reliable.