With the development of the research on inertial confinement fusion (ICF), there is needed a diagnostic technique for low Z materials.The phase contrast imaging, which relies on gradients in the refractive index and wave interference, is proposed to characterize the typical ICF (inertial confinement fusion) capsule shell. In our work it is indicated that the phase contrast imaging obtained with a micro-focus X-ray source provides complementary information about the capsule shell with high resolution 2 upm, and has advantages of absorb imaging. Such a capsule shell diagnostic technique is very useful for ICF diagnoses. Besides, we propose an approach to obtaining of the optimum contrast and spatial resolution in phase contrast imaging. It is a guidance in obtaining an excellent result in phase contrast imaging experiment, and can be widely used in biomedicine, materials science.