Ultra-wideband(UWB) is currently one of three new technologies of wireless communication. Multi-user detection technique is mainly used to eliminate multiple access interference（MAI）in DS-CDMA UWB communication systems. Linear multi-user detection algorithm for multi-access interference suppression or even elimination has certain results. But for a fixed decision threshold is set to 0, the detection performance of linear multi-user detection algorithm will be decreased significantly. Therefore a kind of multi-user detection with pre-processing has been researched. Through the pre-processing, we set dynamic threshold to direct decision the user's data bit information so as to solve the problem the linear multi-user detector’s decision threshold which is fixed impact the detection performance. We may get the global optimal solution though pre-processing of using the thought of the branch and bound algorithm and forcing rules. Then the original problem changes into a smaller multi-user detection problem, in order to get the aim of reducing MAI, increasing the probability of a correct decision and reducing the bit error rate. From the simulation experiment results, it is shown that it has a significant effect in system detection, because after pre-processing the probability of a correct decision has increased, and the bit error rate has been reduced.