The multi-user security transmission scheme on physical layer in a massive multiple-input multiple-output (MIMO) relay based network is studied. There are direct links between the eavesdropper and the source nodes and between the eavesdropper and the relay nodes

so the eavesdropper can receive the signals sent by the source nodes and the relay. The relay employs simple maximum ratio combining in the first stage and maximum ratio transmitting in the second stage by using this scheme and assisted by the null-space artificial noise sent by the relay and the collaboration interference sent by the destination node

security transmission of information between the multi user-pairs is realized even though the channel state information of the eavesdropper cannot be obtained. The secrecy rate and its asymptotic value when the number of antennas of the relay grows to infinity are analyzed. The simulation results show that the secrecy sum rate of the system increases with the number of relay antenna

and eventually reaches the asymptotic value. Furthermore

a considerable secrecy rate can be achieved even if the eavesdropper has the capability to cancel the multi-user interference and to intercept the signals sent by the source nodes and the relay.