In previous studies of polarization-mode-dispersion (PMD) distribution measurement by an optical time-domain reflectometer with polarimetry (p-OTDR), scatterers were assumed to be clouds of nonspherical particles in a fiber. However, the pulsewidth dependence of the degree of polarization (DOP) could not be explained by the assumption of nonspherical backscattering alone. In this paper, it is reported that the p-OTDR waveforms were fitted well by modified Mueller matrices under the assumptions of scattering by cloud of spherical particles and a reduction in the DOP due to the interference of the backscattered waves with the phase fluctuation. A PMD distribution measurement is demonstrated based on the p-OTDR Jones matrix eigenvalue method with the assumption of slowly varying PMD along the fiber length, and the regeneration of the PMD distribution of test fibers fabricated by splicing constituent fibers with known PMDs was successful. Surprisingly, the regenerated PMD distribution along the fiber length shows a linear accumulation of constituent fiber PMD in the short range of 6 km. The reverse-direction measurements show a reasonable regeneration of what is assumed to be a linear accumulation along the fiber length, which strongly suggests that the PMD distribution along the fiber shows a linear accumulation rather than a root-length accumulation in relatively short fibers with smaller PMD.