This paper discusses how to reveal the cognitive operation of human being from the perspective of granular computing, and discusses the uncertainty, ambiguity and other basic issues of cognition, and distinguishes, judges and identifies its link with thought operation. Human brain can only receive messages of different sensory attributes. A thing's state, movement and change process are reflected by its attributes and change process. Set up a granular computing model based on attributes and the judgment criterion change process and work out the basic logic rules for granular computing. The results show that this method can reflect the identification and judgment process with the attributes of uncertainty. At the same time, messages on granular conversion can be fully expressed through the definition of qualitative mapping, so as to better reveal the essential reason for ambiguous cognition of human. This model provides a new convenient tool for the study and stimulation of human's advanced intelligence and image thinking.