The invention provides an efficient key agreement and transmission method, and the method comprises the following steps: a sending party A-caret determines secret information that k1 is an element ofa set {0, 1} in advance; the A-caret has a secret input four-dimensional column vector sigma A, a receiving party B-caret has a secret input four-dimensional column vector sigma B, wherein values of corresponding dimensions of the vector sigma A and the vector sigma B are close; the A-caret performs encoding and sends a piece of four-dimensional encoding information vector V to the B-caret; and the B-caret obtains k2 = k1 through decoding from the vector V and the vector sigma B.