The new era of ejector technology is moving from device scale and entering into system scale. The methodology of the regulation mode of the adjustable ejector has been summarised in this paper. Based on the aerodynamic theory, a performance prediction model for an adjustable ejector under variable operating conditions and variable structures are presented. The regulation characteristics of qualitative regulation and quantitative regulation under different operating modes were researched. The results showed that both quantitative regulation and quantitative regulation have the characteristics of "constant capacity" and the strongly similar characteristics in both regulation modes in form of suction flow rate with varying primary flow rate were discovered. Three different “constant capacity” phenomena in ejectors were found, and the similarity indicated that the turbulent flow in the ejector had some statistical invariances in the form of the mass flow rate of jetting flow. The operating features in qualitative and quantitative combined regulation with varying primary pressure under different primary nozzle opening for adjustable ejector were analysed. In the ideal regulation state in qualitative and quantitative combined regulation, the adjustable ejector can always work on the best performance in critical mode with highest entrainment ratio and efficiency.