The theory of imaginary devices posits that imagination is an activity that occurs at multiple different levels within the human body with a unified goal.This goal is to enable human cognition to transcend the current existence,turning the absent into the present,all of which is encompassed by a virtual imaginary device.The imaginary device is composed of a resource supplier,an imagination generator and an imagination expressor.The resource supplier transports representational resources of different levels,different cognitive units,and different modalities to the imagination generator;The imagination generator generates the results of imagination by operating representational resources through the invocation of imagination rules;The imagination expressor expresses the newly generated imagination in a multi-modal way.The emergence of the imaginary device is the result of the interaction between innate biological foundations and acquired experience.The difference between the results of imagination and reasoning is that the results of imagination are heuristic rather than conclusive.The process of imagination is dynamic and has external effects.The article also provides three theoretical formulas for measuring imagination.