Morphology and microstructure of particulates with the application of different gas compositions in EGR were analyzed by using transmission electron microscope and image processing software (Digital Micrograph). The results show that the particulates with the application of CO2 mainly have the chain structure. The disorder degree of carbon layer in elementary particulate is higher and the content of graphitic crystalline structure in shell is less than those particulates with the application of EGR. Besides, the fringe separation distance has a significant increase. The average fringe length has a significant decrease; the tortuosity is the biggest and the fractal dimension is the smallest. The particulates with the application of N2 mainly have the stone clusters; the elementary particulate integrated more tightly; the core of elementary particulate is more obvious and the content of graphitic crystalline structure in shell is less than those particulates with the application of EGR. Besides that, the fringe separation distance has a significant decrease; the average fringe length has a significant increase; the tortuosity is the smallest and the fractal dimension is the biggest. Those indicate that the structure of particular with the application of N2 is more tightness than those with the application of CO2, and increasing of the content of CO2 in EGR can improve the oxidation ability of particulate and decrease the disorder degree of carbon layer.