The present invention discloses a method and an apparatus for downlink beam forming in a TD-CDMA system. The method includes: acquiring the spatial covariance matrixes of all uplink slot interference user signals and the downlink slots in which the interference user signals locate; obtaining the interference spatial covariance matrixes of each downlink slot based on the downlink slots in which the interference user signals locate and the spatial covariance matrixes of the interference user signals; determining the beam forming weight coefficient of downlink expected user signals based on the interference spatial covariance matrixes of each downlink slot and the spatial covariance matrixes of the downlink expected user signals; implementing beam forming based on the beam forming weight coefficient of downlink expected user signals.