1. A method for Soft-output Fixed-complexity Sphere Decoding (SFSD) detection, comprising: performing QR decomposition on a channel response matrix to acquire a Q matrix and an R matrix; multiplying a conjugate transpose of the Q matrix by a received signal to acquire an equalized signal of the received signal; performing Maximum Likelihood (ML) path detection on the equalized signal, decreasing, layer by layer, reserved nodes in respective layers to acquire an ML path, and reserving branches as many as iterations; performing ML complementary set path detection on the branches, and reserving all nodes of an acquired complementary set layer and decreasing, layer by layer, reserved nodes in other layers to acquire an ML complementary set path; and acquiring Likelihood Ratio (LLR) information of each bit of each symbol of each layer according to the ML path and the ML complementary set path.