The filtration performance of the filter element was compared by using the performance evaluation devices for high-pressure condition in the field and atmospheric pressure in the laboratory. The influences of the physical properties of liquid and the concentration of oil mist on the filter element's filtration performance were analyzed. An improvement method of the filter element was proposed and the improving effect was verified. The results showed that the filtration efficiency of filter element under high pressure was slightly lower than that under atmospheric pressure due to the change of gas-liquid interaction, but the change rule of filtration performance under atmospheric pressure could reflect the actual operation performance on-site. Compared with the gas flowrate, the liquid viscosity had a greater impact on the filtration efficiency of the medium efficiency filter element, and the pressure drop of filter element significantly increased only during filtration for liquid with high viscosity. The effect of oil mist concentration on the pressure drop of such filter element was controlled by the liquid viscosity. The pressure drop increased with the increase of oil mist concentration at high viscosity, but did not change at low viscosity. Due to the influence of flowrate on droplet capture by diffusion effect, the filter efficiency for high viscosity liquid increased with the decrease of oil mist concentration at low flowrate. By adjusting the composition and layout of the filter material inside the filter element, it could achieve efficient capture of small droplets, and the filtration efficiency for dioctyl sebacate droplets was at least 50% higher than that of the original filter element. The research results are of great significance to guide the improvement of filter element performance and understanding of mechanism in the process of natural gas storage and transportation.