In our country, the airworthiness certification and aviation technology are lagging far behind，the development of domestic onboard flame arrester has just been included into the agenda. Hence, based on the analysis of the reason of the pressure drop of the airborne flame arresters, a method suitable for calculating the pressure drop of the airborne flame arresters is proposed. Based on the comparison with the experimental results and the verification of the correctness of the method, according to arresters technical requirements, analyze the pressure drop of flame arrestor element with different characteristic dimension under air flow and fuel overflow, and discuss the influence of various factors on the pressure drop of airborne flame arresters. The results indicate that the proposed method can provide useful reference for engineering design, calculation and selection of airborne flame arresters.