The detection of multiple-input multiple-output (MIMO) system is an important issue. The K-best sphere decoding (K-best SD) is a promising technology for the MIMO detection. But the complexity of the K-best SD is very high. In this article, a new algorithm is proposed to simply the complexity of the K-best SD. Through analyzing the statistics character of the channel matrix, we propose that the number of K can be reduced with the increasing of the detection layers. Simulation results show that with the price of slight performance drop the proposed algorithm can reduce the complexity of the K-best SD efficiently.