This short note is a supplement of ref. [1], it also replies some points in the paper [2]. We emphasize that in the kubo formula if we let v →∞ first and then △t→∞, the correct transport coefficient will be obtained. Expressing the transport coefficient according to the theory of approach to equilibrium can make the coefficient, which is indefinite in mechanical formalism, well definite. It is pointed out that to introduce the macroscopic current operator into the transport theory is unnecessary.