An external airbag system in which the airbags deploy outside the vehicle before a collision has been proposed. The developed system uses four airbags that are mounted inside the front and rear bumpers and both side doors. The problem in this system is “how to control inner pressure of airbags immediately after collision” so as to absorb the crash energy as much as possible. Firstly, a model of inner pressure variation in the airbag was given for this solution from the fluid dynamics standpoint and its simulation was performed by changing the outlet area and the crash load in the airbag system. According to the experiment, this model was basically approximated by the second order transfer function in which the input is a crash load and the output is the resultant inner pressure of the airbag. Secondly, a crash test was implemented at a vehicle speed of less than 50 km/h and the inner pressure change was measured at a collision to the truck tires with several airbag outlet areas. Experimental results show that the damping factor immediately after the collision is one of measures to absorb the crash energy if the outlet area of an airbag is adequately designed. They also suggest