How to put all together is always a big question asked by systems science researchers. We have quite a few approaches to probe the question, and the best one of them is to use models. The purpose of this paper is to show that the All-in-One Model ∞ may be the simplest one. First of all, we have to inquire into the General Systems Theory(GST) or Theory of Everything(TOE). There drive us to the question whether there has the General Systems Model(GSM) or Model of Everything(MOE). It will be useful, to begin with, to make a distinction between three levels of models of theory. The three levels look like a upside-down triangle(▽). The most upper level is full of every kind of models of disciplinary theory, for example, Easton’s politics system model. The middle level is the models of multi-disciplinary theory, or trans-disciplinary theory. Parsons’s social systems model, Holling’s adaptive cycle model and CAS(Complex adaptive Systems) model are notable examples. The lowest level is the model of General Systems Theory, or Theory of Everything. Miller’s living system mode, Wilber’s AQAL model and Ritzer's Integration Model are the illustrations of the same point. There are considerable evidences to prove that the All-in-One Model ∞ may be the simplest one in the lowest level. This article choses some representativeness of models of theory from the three levels, like Cybernetics, Game theory, Systems dynamics, Beer’s VSM, Checkland’s SSM, Flood and Jackson’s TSI, etc., and uses the All-in-One model ∞ to explain them and prove the generative appliance to all models of theory. In the end of article, we propose that All-in-One model ∞ can be used widely in image search engine of www, and open a new method for image searching.