The modulated structure of ${\mathrm{Bi}}_{2.1\mathrm{\ensuremath{-}}\mathrm{y}}$${\mathrm{Pb}}_{\mathrm{y}}$${\mathrm{Sr}}_{1.9\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{La}}_{\mathrm{x}}$${\mathrm{CuO}}_{\mathrm{z}}$ (y=0.2,n0.4;n0.1\ensuremath{\leqslant}x\ensuremath{\leqslant}1.0) was studied by means of electron diffraction. The experimental data show that the modulated structure changes from a mixed Bi/Pb-type to a pure Bi-type modulation with an increasing amount of La content in both the y=0.2 and 0.4 series and that the periodicity of the Bi-type modulation decreases correspondingly. When x=1.0, the modulation exhibits nearly the same characteristic in the samples with y=0.2 and 0.4. In addition, the extra-oxygen behavior, together with the local-structural distortion characteristic, related to the change of the modulated structure was also examined with Raman scattering, x-ray photoelectron spectroscopy and high-resolution electron micro- graphy. The experiment results reveal that there are more extra-oxygen atoms intercalating in the ${\mathrm{Bi}}_{2}$${\mathrm{O}}_{2}$ layers with a decrease in the modulation periodicity in the y=0.2 series. However, for the y=0.4 series, no more extra oxygen is incorporated into the ${\mathrm{Bi}}_{2}$${\mathrm{O}}_{2}$ layers with a decrease in the modulation periodicity, but the degree of local-structural distortion strengthens markedly in the ${\mathrm{Bi}}_{2}$${\mathrm{O}}_{2}$ layers. Based on these experiment results, we discuss the relationship of the superstructure modulation, extra oxygen, and the local-structural distortion.