A method for detecting a signal, used in a multi-input multi-output (MIMO) communications system, including: receiving a vector associated with data bits transmitted from the MIMO communications system; finding a first layer from the received vector according to a determining condition, wherein the received vector includes multiple layers, and the multiple layers include the first layer and remaining layers; performing a first scanning procedure for the multiple layers of the received vector to obtain log likelihood ratios (LLR) corresponding to the data bits transmitted from the remaining layers; obtaining a received vector of the first layer according to an equivalent received vector of the remaining layers; and performing a second scanning procedure on data bits of the first layer according to the received vector of the first layer to generate an LLR corresponding to the data bits of the first layer.