Self-assembled InP/InAs/InP quantum wires have been successfully stacked for 10 vertical periods and characterized based on photoluminescence (PL) studies. Compared with single-period quantum wires, unique behaviors appear in the PL spectra and some fundamental effects have been observed. Through the detailed analyses of the PL shapes, linewidths, and polarizations at different pump wavelengths, pump intensities and sample temperatures, it is evidenced that the wire width and subband energy gradually decrease while the average wire thickness increases from the bottom period to the top one, period by period. Meanwhile, the average wire width gradually decreases. In addition, from the bottom to the top period the size fluctuation within each period decreases. Furthermore, above certain temperature or pump intensity all the quantum wires are vertically coupled among one another. Following these results, new growth conditions have been suggested, which can be essential to improving the optical quality of these self-assembled quantum wires.