A beam-forming apparatus applied in a Multiple Input Multiple Output (MIMO) system and a related method where the MIMO system transmits signals through a plurality of channels. The method includes generating a plurality of channel estimations corresponding to the channels; determining a plurality of first candidate transmitting vectors; selecting a first transmitting vector from the first candidate transmitting vectors according to the channel estimations; determining a plurality of second candidate transmitting vectors orthogonal to the first transmitting vector; selecting a second transmitting vector from the second candidate transmitting vectors according to the channel estimations; generating a plurality of transmitted signals by combining a first data stream and a second data stream according to the first and second transmitting vectors; and respectively transmitting the transmitted signals through a plurality of antennas. The apparatus ensures that power of a data stream is distributed equally for each antenna.