Sphere decoder has been introduced to the multiple-input-multiple-output (MIMO) communication systems, with which the maximum likelihood (ML) detection becomes feasible. In order to combine the sphere decoders with the outer channel code decoder, researchers have proposed to include a candidate list in the sphere decoder to provide soft information to the channel code decoder. This algorithm is called list sphere decoder (LSD). In the LSD, different from the conventional sphere decoder (CSD), the candidate list introduces significant hardware overhead. In this paper, we propose to use a tree-type comparator array, a link table and sublists to reduce the hardware complexity of inserting new candidates into the list. Combining these techniques, we can reduce the complexity by around 90% compared with the straightforward implementations.