Abstract: The successive interference cancellation (SIC) receiver is widely used in the Multi-Input-Multi-Output (MIMO) system as a signal detection technology. In the SIC receiver, the decision error of the detected streams will impact the accuracy of the undetected streams, which will bring in residual multi-stream interference and cause the error diffusion problem. In this paper, a minimum mean square error-ordered successive interference cancellation (MMSE-OSIC) receiver with soft decision (SD) is presented. In the proposed SD-MMSE-OSIC receiver, the soft decision instead of the hard decision is used for interference regeneration and cancellation, which can efficiently prevent the error diffusion problem of the hard decision (HD) based MMSEOSIC receiver. We also propose a method to estimate the power of the residual multi-stream interference, with which we can accurately estimate the signal-to-interference-and-noise ratio (SINR) of each stream, which is usually overestimated in the HD based MMSE-OSIC receiver. In the proposed receiver, the soft decision method with higher reliability is utilized to minimize the residual multi-stream interference, while the accurate estimation of SINR helps to mitigate the impact of the residual interference on the undetected streams, thus fewer error diffusion problems are assured. Simulation results show that the proposed SD-MMSE-OSIC receiver significantly outperforms the linear MMSE receiver and the hard decision based MMSE-OSIC receiver.