In terms of the improved brick-wall model, the statistical entropy of Dirac field in the most general spherically symmetric non-static black hole is calculated. It is shown that the entropy of the black hole is proportional to the area of event horizon at any time. It is noteworthy that the calculating formula for the dynamic proportional coefficient is obtained in this paper. Through calculating these dynamic proportional coefficients, the statistical entropies of the Dirac field in all kinds of the spherically symmetric non-static black hole can be obtained directly.