In order to overcome the difficulty in the online and non-destructive measurement of engine cylinder's intake airflow field caused by its invisibility and dynamic characteristics,a tomographic image diagnosis method is proposed.In the investigation,first,the principles of industrial computer tomography ( ICT) for obtaining the tomographic image of diesel engine cylinder's intake airflow field are analyzed.Then,the behaviors of airflow field's trace point,density,velocity and velocity variation in the tomographic image are discussed,and the segmentation pre-treatment methods of the cylinder intake system's tomographic image are explored based on the maximum average mutual information.Moreover,an extraction method of multi-target image features ofthe intake airflow field is presented based on the mutual information of random variables.Finally,the information of the airflow field's trace point,density,flow velocity and velocity variation status inside confined spaces are non-destructively extracted in realtime from the high-energy ICT images of a single-cylinder vertical diesel engine,and the tomographic chain structure and its shape formed by the gas-cylinder and gas-gas interactions in the flow process are discovered.It is found that the proposed tomographic image diagnosis method is more suitable for the nondestructive,online and multi-dimension diagnosis than the existing methods.