The interaction between light and plasma is one of the key problems in an inertial confinement fusion system.Some instability processes will occur when the energy of laser is absorbed by plasma. Because reducing the coherence of laser can significantly restrain the instability of the plasma, in practice, a continuous phase plate(CPP) is often used to generate the speckle and thereby to restrain the nonlinear effect in plasma. To clarify the working mechanism of CPP, the propagation characteristics of speckl...