With the rapid development of 5G communication technology, network security has become a major concern. In the context of 5G, the security of encryption and authentication algorithms is of utmost importance. This research focuses on 5G communication security and presents the design of a cryptographic coprocessor for the ZUC-256 cipher algorithm. ZUC-256 is a byte-oriented stream cipher algorithm that provides 256-bit security and is widely used for encryption and authentication in 5G communication. However, there is limited research on hardware implementations of the ZUC-256 algorithm, especially for resource-constrained devices. This paper leverages the RISC-V architecture processor, known for its simplicity and scalability, to design the ZUC-256 stream cipher coprocessor. To enhance the efficiency of keystream generation, targeted design and optimization techniques are applied to the hardware implementation of the ZUC-256 algorithm. Through the synergy of software and hardware for encryption and decryption, efficient and secure 5G communication applications are achieved. Experimental results demonstrate that the designed ZUC-256 cryptographic coprocessor exhibits excellent performance and reliability in 5G communication security. Its high throughput and low power consumption make it suitable for resource-constrained devices.