A method for transmitting data by applying a precoding matrix in an open-loop multiple input multiple output (MIMO) system is disclosed. The method comprises selecting a precoding matrix and applying the selected precoding matrix to data during initial transmission; selecting a precoding matrix and applying the selected precoding matrix to data to be retransmitted; and retransmitting the data to which the precoding matrix is applied, wherein an index of the precoding matrix applied to the data is determined based on the times of current retransmission times of the data and index of the precoding matrix applied during initial transmission of the data.