Embodiments of the present invention provide a method, an apparatus, and a system for signal transmission. The method includes: obtaining, by a base station, a high-power precoding matrix and a low-power precoding matrix according to channel quality information, precoding a corresponding high-power signal stream according to the high-power precoding matrix respectively to obtain a first signal stream, precoding a corresponding low-power signal stream according to the low-power precoding matrix respectively to obtain a second signal stream, superimposing the first signal stream and the second signal stream to obtain one or more superimposed signal streams and transmitting the one or more superimposed signal streams to user terminals; decoding, by the user terminals, the received one or more superimposed signal streams by using receiving matrices, and obtaining signal streams that the user terminals need. The embodiments of the present invention are applicable to signal transmission in a Multiple-Input Multiple-output system.