The study of the energy absorption characteristics of expansion tube–oil–gas combined landing gear is critical for the crashworthiness design of helicopters. This paper considers the expansion tube–oil–gas combined landing gear as an integrated system and establishes a novel dynamic model based on the principles of rigid body dynamics. The accuracy of the simulation model is validated through drop impact tests, enabling an in-depth investigation of the landing gear's crash resistance under impact conditions. The results indicate that when the expansion force reaches 29 kN and the impact velocity is 10 m/s, the energy absorbed by the expansion tube accounts for 74.6% of the total, while the oil–gas damper absorbs the remaining 25.4%. This highlights the dominant role of the expansion tube in energy dissipation. Further analysis reveals that the expansion force of the expansion tube can modulate the energy absorption ratio between the oil–gas damper and the expansion tube, providing valuable insights for the structural design of helicopter crashworthy systems.