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Massive multiple-input multipie-output provides improved energy efficiency and spectral efficiency in 5G.However it requires large-scale matrix computation with tremendous complexity,especially for data detection and precoding.Recently,many detection and precoding methods were proposed using approximate iteration methods,which meet the demand of precision with low complexity.In this paper,we compare these approximate iteration methods in precision and complexity,and then improve these methods with iteration refinement at the cost of little complexity and no extra hardware resource.By derivation,our proposal is a combination of three approximate iteration methods in essence and provides remarkable precision improvement on desired vectors.The results show that our proposal provides 27％-83％ normalized mean-squared error improvement of the detection symbol vector and precoding symbol vector.Moreover,we find the bit-error rate is mainly controlled by soft-input soft-output Viterbi decoding when using approximate iteration methods.Further,only considering the effect on soft-input soft-output Viterbi decoding,the simulation results show that using a rough estimation for the filter matrix of minimum mean square error detection to calculating log-likelihood ratio could provide enough good bit-error rate performance,especially when the ratio of base station antennas number and the users number is not too large.