Based on the Gross-Pitaevskii theory,for a Bose-condensed gas confined in a har-monic trap and in a one-dimensional(1D)optical lattice,the relationship of the Gaussian width of the sub-condenses and the intensity of 1D-optical lattices potential is studied by using the G-P energy functional and the variational method. For the ideal non-interacting model,the Gaussian width of the sub-condenses is analyzed. Concerning interacting Bose-condensed atoms,the Gaussian approximate model is advanced and the analytic expression of the Gaussian width with the intensity of optical lattices potential is obtained. And then,those analytical results are compared with the straightforward numerical calculation. It indicates that the Gaussian approximate model is closer to the results of the numerical solution,and both are reaching unanimity with the intensity of 1D-optical lattices potential increasing.