Abstract: The pneumatic-vibratory probe compaction method is a new technology for the treatment of collapsible loess. By using the self-developed pneumatic-vibration model test devices, the model tests on the reinforcement of collapsible loess are carried out by the above method under two test conditions, single excitation force and air jet combined with excitation force. The reinforcement effects are evaluated. The change rules of the horizontal soil pressure, vertical vibration velocity of soil particles and gas pressure values in the soils during the penetration of the vibratory probe are studied. The results show that the density of soil layers at each depth is significantly increased, and the collapsibility coefficient is reduced after the treatment. With the addition of air jet, the density of the soil layers below 100 mm in depth is further increased, and the maximum horizontal soil pressure is increased by 20.4%. At the same time, the vibration response of soils caused by the method is amplified. The mechanism of air jet in the process of soil reinforcement is revealed, and the mechanism of the pneumatic-vibratory probe compaction method to reinforce collapsible loess is discussed, which provides the theoretical basis for promoting the application of the method to treat collapsible loess foundation.