In the device-to-device (D2D) caching network, the number of cache replicas is an important factor that restricts the caching efficiency of the system. Excessive replicas cannot make full use of the cache resources while insufficient replicas make it difficult for popular files to be obtained effectively. To address the issue of cache replicas placement (CRP) in D2D cache networks, utilizing the convex programming theory, we design a CRP  scheme with the goal of maximizing the cache hit ratio of the system. Simulation results show that compared with existing replicas placement schemes the proposed scheme can effectively improve the overall cache hit rate of the D2D cache network.