A method to predict the change of the cushion pressure and the bag skirt configuration of ACV in heave is proposed. It is a quasistatic analysis based on the analysis of the skirt configuration in static operation that was proposed by the present authors. The cushion pressure depends on the velocity of motion as well as the hoverheight. It is higher in the downward motion than in the upward motion with the same hoverheight. As the model approaches the ground surface, the bag skirt is pushed outwards and also upwards but the hoverheight still decreases. This produces the increase of the cushion pressure that also flattened the configuration of the bag. The outward displacement of the bag produces the additional increase of the cushion base area and increases the restoring force. The stability is then increased.