This paper presents similarity analysis of two running states of antenna pointing mechanism (APM) in space and on the air bearing simulator with load based on similarity theory. The running states of APM in space and on the air bearing simulator are described. The structure of air bearing simulator is introduced briefly. The similarity rules of APM running state are derived. Because the running state of APM on the simulator is not strictly similar with the running state in space, the degree of approximate similarity is calculated by deriving the item quantity degree of similarity and numerical degree of similarity. The parameters affecting the degree of similarity are analyzed and the main parameters are found to improve the degree of similarity.