Abstract: Sparse code multiple access (SCMA) is a competitive air-interface technology in fifth generation (5G) mobile communication, which can enhance spectrum efficiency and support massive connections. Due to the random feature of channels between base station and users, the performance of SCMA system will be promoted by adaptively adjusting transmitted codebook of users according to the condition of channel gain. Codebook assignment based on fixed resource nodes order and codebook assignment based on dynamic resource nodes order are proposed to solve the problem of codebook assignment optimization. Simulation results show that proposed algorithms can obviously improve bit error ratio (BER) performance and maintain the same convergence rate compared with conventional random codebook assignment.