A method for sending channel information, characterized by comprising: a mobile terminal acquiring channel information; according to the channel information, determining, in a codebook space, a Rank Indicator and a Precoding Matrix Indicator corresponding to the channel information; and sending the RI and the PMI to a base station; wherein when the RI is equal to 7, a codebook space is constructed by selecting any 4 matrixes from a set as follows: the set is { Z 1 X 1 Z 1 − X 1, Z 1 X 1 − Z 1 X 1, Z 2 X 2 Z 2 − X 2, Z 2 X 2 − Z 2 X 2, Z 3 X 3 Z 3 X 3, Z 3 X 3 − Z 3 X 3, Z 4 X 4 Z 4 − X 4, Z 4 X 4 − Z 4 X 4}, wherein Z 1 and Z 2 are both 4×3 matrixes, Z 1 is composed of any 3 columns in X 1, Z 2 is composed of any 3 columns in X 2, Z 3 is composed of any 3 columns in X 3, and Z 4 is composed of any 3 columns in X 4; or Z 1 is composed of any 3 columns in X 1, Z 2 is composed of any 3 columns in X 3, Z 3 is composed of any 3 columns in X 2, and Z 4 is composed of any 3 columns in X 4, wherein X 1 = 1 1 1 1 1 j − 1 − j 1 − 1 1 − 1 1 − j − 1 j, X 2 = 1 1 1 1 q 1 q 2 q 3 q 4 i − i i − i q 2 q 1 q 4 q 3 q 1 = 1 + i 2, q 2 = − 1 + i 2, q 3 = − 1 − i 2, q 4 = 1 − i 2 X 3 = 1 1 1 1 e j π 8 e j 5 π 8 e j − 7 π 8 e j − 3 π 8 e j 2 π 8 e j 10 π 8 e j − 14 π 8 e j − 6 π 8 e j 3 π 8 e j 15 π 8 e j − 21 π 8 e j − 9 π 8, X 4 1 1 1 1 e j 3 π 8 e j 7 π 8 e j − 5 π 8 e j − π 8 e j 6 π 8 e j 14 π 8 e j − 10 π 8 e j − 2 π 8 e j 9 π 8 e j 21 π 8 e j − 15 π 8 e j − 3 π 8; or, when the RI is equal to 6, a codebook space is constructed by 4 matrixes Z 1 Z 1 Z 1 − Z 1, Z 2 Z 2 Z 2 − Z 2, Z 3 Z 3 Z 3 − Z 3 and Z 4 Z 4 Z 4 − Z 4, wherein Z 1 and Z 2 are both 4×3 matrixes, Z 1 is composed of any 3 columns in X 1, and Z 2 is composed of any 3 columns in X 2, X 1 = 1 1 1 1 1 j − 1 − j 1 − 1 1 − 1 1 − j − 1 j, X 2 = 1 1 1 1 q 1 q 2 q 3 q 4 i − i i − i q 2 q 1 q 4 q 3, q 1 = 1 + i 2, q 2 = − 1 + i 2, q 3 = − 1 − i 2, q 4 = 1 − i 2; Z 3 is composed of any 3 columns in X 3, and Z 4 is composed of any 3 columns in X 4, X 3 = 1 1 1 1 e j π 8 e j 5 π 8 e j − 7 π 8 e j − 3 π 8 e j 2 π 8 e j 10 π 8 e j − 14 π 8 e j − 6 π 8 e j 3 π 8 e j 15 π 8 e j − 21 π 8 e j − 9 π 8, X 4 1 1 1 1 e j 3 π 8 e j 7 π 8 e j − 5 π 8 e j − π 8 e j 6 π 8 e j 14 π 8 e j − 10 π 8 e j − 2 π 8 e j 9 π 8 e j 21 π 8 e j − 15 π 8 e j − 3 π 8. a mobile terminal acquiring channel information; according to the channel information, determining, in a codebook space, a Rank Indicator and a Precoding Matrix Indicator corresponding to the channel information; and sending the RI and the PMI to a base station; wherein when the RI is equal to 7, a codebook space is constructed by selecting any 4 matrixes from a set as follows: the set is { Z 1 X 1 Z 1 − X 1, Z 1 X 1 − Z 1 X 1, Z 2 X 2 Z 2 − X 2, Z 2 X 2 − Z 2 X 2, Z 3 X 3 Z 3 X 3, Z 3 X 3 − Z 3 X 3, Z 4 X 4 Z 4 − X 4, Z 4 X 4 − Z 4 X 4}, wherein Z 1 and Z 2 are both 4×3 matrixes, Z 1 is composed of any 3 columns in X 1, Z 2 is composed of any 3 columns in X 2, Z 3 is composed of any 3 columns in X 3, and Z 4 is composed of any 3 columns in X 4; or Z 1 is composed of any 3 columns in X 1, Z 2 is composed of any 3 columns in X 3, Z 3 is composed of any 3 columns in X 2, and Z 4 is composed of any 3 columns in X 4, wherein X 1 = 1 1 1 1 1 j − 1 − j 1 − 1 1 − 1 1 − j − 1 j, X 2 = 1 1 1 1 q 1 q 2 q 3 q 4 i − i i − i q 2 q 1 q 4 q 3 q 1 = 1 + i 2, q 2 = − 1 + i 2, q 3 = − 1 − i 2, q 4 = 1 − i 2 X 3 = 1 1 1 1 e j π 8 e j 5 π 8 e j − 7 π 8 e j − 3 π 8 e j 2 π 8 e j 10 π 8 e j − 14 π 8 e j − 6 π 8 e j 3 π 8 e j 15 π 8 e j − 21 π 8 e j − 9 π 8, X 4 1 1 1 1 e j 3 π 8 e j 7 π 8 e j − 5 π 8 e j − π 8 e j 6 π 8 e j 14 π 8 e j − 10 π 8 e j − 2 π 8 e j 9 π 8 e j 21 π 8 e j − 15 π 8 e j − 3 π 8; or, when the RI is equal to 6, a codebook space is constructed by 4 matrixes Z 1 Z 1 Z 1 − Z 1, Z 2 Z 2 Z 2 − Z 2, Z 3 Z 3 Z 3 − Z 3 and Z 4 Z 4 Z 4 − Z 4, wherein Z 1 and Z 2 are both 4×3 matrixes, Z 1 is composed of any 3 columns in X 1, and Z 2 is composed of any 3 columns in X 2, X 1 = 1 1 1 1 1 j − 1 − j 1 − 1 1 − 1 1 − j − 1 j, X 2 = 1 1 1 1 q 1 q 2 q 3 q 4 i − i i − i q 2 q 1 q 4 q 3, q 1 = 1 + i 2, q 2 = − 1 + i 2, q 3 = − 1 − i 2, q 4 = 1 − i 2; Z 3 is composed of any 3 columns in X 3, and Z 4 is composed of any 3 columns in X 4, X 3 = 1 1 1 1 e j π 8 e j 5 π 8 e j − 7 π 8 e j − 3 π 8 e j 2 π 8 e j 10 π 8 e j − 14 π 8 e j − 6 π 8 e j 3 π 8 e j 15 π 8 e j − 21 π 8 e j − 9 π 8, X 4 1 1 1 1 e j 3 π 8 e j 7 π 8 e j − 5 π 8 e j − π 8 e j 6 π 8 e j 14 π 8 e j − 10 π 8 e j − 2 π 8 e j 9 π 8 e j 21 π 8 e j − 15 π 8 e j − 3 π 8.