Abstract: In this paper, we propose a joint design scheme of multi-relay Physical-layer Network Coding (PNC) system with encryption technology and channel coding to solve the problems of multi-relay communication system such as the throughput decreasing, high Bit Error Rate (BER) and poor security performance. In the proposed scheme, we first introduce the three-relay two-way PNC transmission mode. The working principle of encryption algorithm and communication system collaboration is described. We then propose a joint system model of PNC, Low-Density Parity-Check (LDPC) code and encryption algorithm for the three-relay communication system. Numerical results show that the introduction of encryption technology can effectively guarantee the security of data transmission and reduce the performance loss caused by information transmission and channel eavesdropping in multi-relay system. The introduction of LDPC code, the BER of system is significantly reduced, the decryption ability of system is improved, the effectiveness and reliability of transmission for multi-relay system are effectively improved.