To enhance the spectral efficiency of non-orthogonal multiple access (NOMA) in massive multiple input multiple output systems, we propose a user pairing and pair scheduling algorithm, which can, simultaneously, pair the selected users and schedule suitable user pairs for data transmission. Through dividually selecting the first user and the second user for each user pair, the proposed algorithm can make sure that both the two users in each user pair can make the greatest contribution to the system sum rate. To suppress the inter-pair interference, we design an interference cancellation combining (ICC) matrix, which first breaks through the constraint between antenna numbers of base station and users. Theoretical analyses and computer simulations show that, the proposed algorithm has excellent sum rate and outage performance compared with the traditional user pairing algorithms.