A multi-user multi-input multi-output (MIMO) method for transmitting signal with a includes: performing a Tomlinson-Harashima pre-coding (THP) on raw data; decomposing a channel matrix to a product of a block triangular matrix and a unitary matrix, and generating a signal to be transmitted by performing a forward filtering on the THP coded data by using the unitary matrix. A multi-user MIMO apparatus for transmitting signal includes an interference pre-eliminating unit, a modulo unit, a forward filtering unit, and a channel matrix decomposing unit. A multi-user MIMO communication system is further provided.