The effects of the periodical time-dependent perturbation on a KdV (Korteweg de Vries) soliton are studied. Expanding the perturbation term into a Fourier series, we find that the time-independent term will lead to the secular terms. In this paper, the soliton parameters (height, width and velocity) are derived by eliminating the secular terms, and the corrections on a soliton caused by perturbation are obtained with the help of other terms in Fourier series in the first-order approximation.