The purpose of situation understanding is to identify the intention and warfare plan of enemy, which explains the current situation based on the expert knowledge and situation character vector. The battlefield circumstances in the modern aerial defence warfare become more and more intricate, and the aerial intelligence obtained is uncertain, so the effective inference of intention of the air attack is an important problem in the C4ISR system. In this paper, the uncertain aerial intelligence is expressed by the interval number. The distance formula between interval number and real number is presented. The target intention is described by the characters of position angle, distance, horizontal speed, course angle and height. Then the inference of intention model based on interval number grey relationship analysis with uncertain aerial intelligence is built. Taking the target intention to be inferred as the comparative sequence, and the known normal character vector as the reference sequence, the normal character number can be calculated by the method of fuzzy cluster analysis. The validity of this method is demonstrated by an example, which can provide scientific basis for the command decision making in the aerial defence warfare.