A method for forming Time Division Duplex, TDD, Multi-Input Multi-Output, MIMO, downlink beams, wherein the method comprises: by a Base Station, BS, receiving an index of a codebook element from a mobile terminal, wherein the codebook element refers to a codebook element whose correlation value has a greatest modulus value among correlation values that are calculated by the mobile terminal and are about correlation between the codebook element and a downlink channel corresponding to a non-transmitting antenna of the mobile terminal, wherein an eigenvector of the transmitting correlation matrix or an orthogonal random codebook is used as the codebook; calculating a downlink channel vector corresponding to the non-transmitting antenna of the mobile terminal according to the index of the codebook element whose correlation value has the greatest modulus value; measuring an uplink channel vector of a transmitting antenna of the mobile terminal, and regarding the uplink channel vector as the downlink channel vector corresponding to the transmitting antenna of the mobile terminal according to uplink-downlink channel symmetry of a TDD system; and performing Singular Value Decomposition, SVD, by using downlink channel vectors of antennas of the mobile terminal to determine a best transmitting precoding matrix, wherein the downlink channel vectors of the antennas of the mobile terminal are composed of the downlink channel vector corresponding to the non-transmitting antenna of the mobile terminal and the downlink channel vector corresponding to the transmitting antenna of the mobile terminal, wherein the calculating a downlink channel vector corresponding to the non-transmitting antenna of the mobile terminal further comprises: calculating, by the BS, the downlink channel vector corresponding to the non-transmitting antenna of the mobile terminal through a Constraint Maximum Likelihood, CML, estimation method, wherein the CML estimation method represents a Maximum Likelihood estimation method on the basis of a constraint, subjected by the BS when performing precoding, that there are only Partial Channel State Information, PCSI, corresponding to transmitting antennas of the mobile terminal and channel statistic information of non-transmitting antennas, wherein a same codebook is maintained on the mobile terminal and the BS simultaneously, and length of the codebook is equal to the number of transmitting antennas of the BS. by a Base Station, BS, receiving an index of a codebook element from a mobile terminal, wherein the codebook element refers to a codebook element whose correlation value has a greatest modulus value among correlation values that are calculated by the mobile terminal and are about correlation between the codebook element and a downlink channel corresponding to a non-transmitting antenna of the mobile terminal, wherein an eigenvector of the transmitting correlation matrix or an orthogonal random codebook is used as the codebook; calculating a downlink channel vector corresponding to the non-transmitting antenna of the mobile terminal according to the index of the codebook element whose correlation value has the greatest modulus value; measuring an uplink channel vector of a transmitting antenna of the mobile terminal, and regarding the uplink channel vector as the downlink channel vector corresponding to the transmitting antenna of the mobile terminal according to uplink-downlink channel symmetry of a TDD system; and performing Singular Value Decomposition, SVD, by using downlink channel vectors of antennas of the mobile terminal to determine a best transmitting precoding matrix, wherein the downlink channel vectors of the antennas of the mobile terminal are composed of the downlink channel vector corresponding to the non-transmitting antenna of the mobile terminal and the downlink channel vector corresponding to the transmitting antenna of the mobile terminal, calculating, by the BS, the downlink channel vector corresponding to the non-transmitting antenna of the mobile terminal through a Constraint Maximum Likelihood, CML, estimation method, wherein the CML estimation method represents a Maximum Likelihood estimation method on the basis of a constraint, subjected by the BS when performing precoding, that there are only Partial Channel State Information, PCSI, corresponding to transmitting antennas of the mobile terminal and channel statistic information of non-transmitting antennas, wherein a same codebook is maintained on the mobile terminal and the BS simultaneously, and length of the codebook is equal to the number of transmitting antennas of the BS.