Polycrystalline CdSSe nanowires were prepared with a low-temperature physical evaporation method. Structural analysis combining HRTEM with XRD demonstrate that these as-prepared wires have a hexagonal wurtzite structure with a polycrystalline nature. Locally excited optical measurements show that though these wires can still act as waveguide cavities, their polycrystalline nature will induce a significant redshift of the emitted light during its transportation along them. Power dependent photoluminescence measurement shows that these polycrystalline wires can achieve broadband coherent emission at the band-edge band under high excitation, which shows marked contrast with the much narrower and multimode spectra observed in the single-crystalline nanowires with the same elemental composition. Time-resolved photoluminescence further confirms the occurrence of coherent emission in these wires, which originates from the electron-hole plasma (EHP) recombination of high-density carriers generated under high excitation. These kinds of polycrystalline alloy nanowires with broadband coherent emission should have potential uses in nano-scaled wavelength tunable light-emitting devices.