multiple-input multiple-output (MU-MIMO) systems is proposed in this paper. This paper constructs a cycle-free fator graph by puncturing certain non-zero entries in a transformed channel matrix, and proposes an adjusted BP algorithm with a more exact a posteriori message updating equation. The proposed algorithm converges rapidly in several iterations due to the cycle-free structure in the factor graph. Nevertheless, puncturing brings distorted noise and thus leads to performance degradation. To tackle this issue, this article further designs a layered detection with the help of maximum likelihood detector ( MLD). Simulations demonstrate that the proposed detection algorithm achieves the identical performance to MLD with much lower complexity.