Non-Orthogonal Multiple Access（NOMA） is a basic support technology for the 5 G wireless networks. It can meet the heterogeneous requirements of large-scale connectivity and high throughput with increasing number of access subscriber. The key idea of NOMA is that the same resource block provides services for multiple users. The supported number of users can be increased. However

the upgrade of system capacity is limited. To solve this issue

the paper combines NOMA technology with massive Multiple-input Multiple-output（MIMO） antenna to improve the capacity of the system. At the same time

the downlink multi-users perform user matching according to channel differences

and the two are divided into one cluster. Block Diagonalization（BD） algorithm is used to eliminate the interference between the clusters. The interference between users in the cluster is eliminated by serial interference. The simulation results show that the BD precoding at the transmitter side can reduce the interference received by the terminal. The system capacity based on NOMA technology combined with massive MIMO is greatly improved. The system performance can be further improved when user matching grouping is performed on this basis.