Abstract: In order to understand the effect of imaging lenses on imaging quality of proton radiograph, the research on the secondary proton-removing effect of imaging lenses has been carried out. The analytical results show that, the secondary protons’ energy is below one half of the original protons’ and the imaging lenses have the ability to remove secondary protons out of the detecting area. The simulation of the whole proton radiography system shows that the imaging lenses have decreased the relative optical path difference caused by secondary protons to less than 2%，and thus the image quality has been improved greatly. Thus the imaging lenses are important components in proton radiography.