In this paper, the characteristics of optical parametric chirped pulse amplification(OPCPA) are numerically studied by a computer- The infection of the group velocity mismatch, the phase-velocity mismatch, and the cubic nonlinearity in the process of amplification has been discussed respectively- The comparison between the OPCPA and the chirped-pulse amplification(CPA) is made, such as of the mechanism of amplification, the synchronization, the red-shift phenomenon, the gain-narrowing effect, and so on- To realize the fast ignition of inertial confinement fusion, we have designed an OPCPA system for the “Shenguang-Ⅱ” facility, which can generate pulse with a duration as short as 50fs and a power of multi-petawatt-