When designing the retractable landing gear of aircraft oil-gas mixed type, the medium flow characteristics between the inner cavities should be fully considered, and the damping aperture and fuel filling amount of a certain UAV landing gear buffer should be taken as the research object, and the single factor experimental method was used to analyze the changes of gas-liquid flow inside the buffer caused by each factor, and the gas-liquid characteristics of the buffer under different damping apertures and oil filling amounts in the lowering stage were simulated and calculated by Fluent software, and the results showed that the damping hole oil flow during the landing gear lowering process is only related to the size of the pore size, not affected by the oil filling amount of the buffer, the damping hole flow rate in the buffer is not related to the liquid level height of the upper cavity of the buffer during the buffer is lowered, the smaller the damping pore diameter, the smaller the flow rate, but the oil filling time is affected by the oil filling amount and pore size, the more oil filling, the less oil required for the lower cavity of the buffer, the shorter the gas-liquid filling time. Under the 637ml oil filling required by this type of UAV, the buffer oil filling time under the 6mm aperture has reached 131s, which exceeded the 2 minutes required for the completion of gas-liquid filling of the buffer cavity of the landing gear of this model, which affects the landing gear buffer performance of the aircraft landing stage, so for the landing gear of this model, the buffer damping aperture should be greater than 6mm. For other types of landing gear buffers, when the oil filling amount is determined, the gas-liquid filling of the buffer that meets the drop stage should be used as one of the buffer damping hole design criteria.