Cryptographic technology is the foundation of cloud computing security. The high-performance cryptographic cards supporting SR-IOV virtualization technology are suitable for cloud cipher machines, which can realize the encryption protection of virtualization data for cloud computing environments and meet the security requirements. However, these cryptographic cards have unsatisfactory compatibility, limited expansibility, poor migration, and low cost performance when applied in cloud cipher machines. Thus, this study proposes a software virtualization method of cryptographic cards based on an I/O front-end and back-end model. With shared memory or virtio as the communication mode, it completes the efficient communication between multiple virtual machines and the host by designing the front-end and back-end driver or service program of cryptographic cards and realizes that common cryptographic cards can be shared by multiple virtual machines. This method can effectively lower the hardware threshold of cloud cipher machines and makes cryptographic cards possess good compatibility and expansibility and high performance, thus showing broad application prospects in information technology applications and innovation.